AnaGram interim repo (temporary): doc/misc/html/gloss.html annotate

annotate doc/misc/html/gloss.html @ 0:13d2b8934445

Import AnaGram (near-)release tree into Mercurial.

author	David A. Holland
date	Sat, 22 Dec 2007 17:52:45 -0500
parents
children

rev	line source
0 13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	2 <HTML>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	3 <HEAD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	4 <TITLE>Glossary of Parsing Terms</TITLE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	5
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	6 </HEAD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	7
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	8 <BODY BGCOLOR="#ffffff" BACKGROUND="tilbl6h.gif"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	9 TEXT="#000000" LINK="#0033CC"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	10 VLINK="#CC0033" ALINK="#CC0099">
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	11
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	12 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	13 <IMG ALIGN="right" SRC="images/agrsl6c.gif" ALT="AnaGram"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	14 WIDTH=124 HEIGHT=30>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	15 <BR CLEAR="RIGHT">
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	16 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	17
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	18 Back to <A HREF="index.html">Index</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	19 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	20 <IMG ALIGN="bottom" SRC="images/rbline6j.gif" ALT="----------------------"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	21 WIDTH=1010 HEIGHT=2 >
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	22
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	23 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	24 <H2>Glossary of Parsing Terms</H2>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	25 <IMG ALIGN="bottom" SRC="images/rbline6j.gif" ALT="----------------------"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	26 WIDTH=1010 HEIGHT=2 >
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	27 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	28
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	29 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	30 <TABLE WIDTH="100%" ALIGN="center" CELLPADDING=15 CELLSPACING=15>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	31 <TR ALIGN="left">
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	32
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	33 <TD VALIGN=TOP NOWRAP WIDTH="50%">
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	34
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	35
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	36
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	37 <A HREF="#ParserAction">Action</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	38 <A HREF="#AcceptAction">Accept Action</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	39 <A HREF="#Associativity">Associativity</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	40 <A HREF="#Backtracking">Backtracking</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	41 <A HREF="#BNF">Backus-Naur Form</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	42 <A HREF="#BinaryOperator">Binary operator</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	43 <A HREF="#Binding">Binding</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	44 <A HREF="#CharacterSets">Character sets</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	45 <A HREF="#Universe">Character Universe</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	46 <A HREF="#CharacteristicRule">Characteristic Rule</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	47 <A HREF="#CharacteristicToken">Characteristic Token</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	48 <A HREF="#SetComplement">Complement of a set</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	49 <A HREF="#CompletedRule">Completed Rule</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	50 <A HREF="#Conflict">Conflict</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	51 <A HREF="#ContextFreeGrammar">Context Free Grammars</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	52 <A HREF="#DefaultReduction">Default reductions</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	53 <A HREF="#SetDifference">Difference of two sets</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	54 <A HREF="#ErrorAction">Error Action</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	55 <A HREF="#EventDriven">Event Driven Parser</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	56 <A HREF="#ExpansionRule">Expansion Rule</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	57 <A HREF="#Grammar">Grammar</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	58 <A HREF="#GrammarAnalysis">Grammar Analysis</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	59 <A HREF="#GrammarRule">Grammar Rule</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	60 <A HREF="#GrammarToken">Grammar Token</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	61 <A HREF="#SetIntersection">Intersection</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	62 <A HREF="#LALRParsing">LALR parsing</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	63 <A HREF="#LexicalScanner">Lexical Scanner</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	64 <A HREF="#Lookahead">Lookahead Token</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	65 <A HREF="#LRParsing">LR Parsing</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	66 <A HREF="#MarkedRule">Marked Rule</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	67 <A HREF="#NonAssociative">Non-associative</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	68 </TD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	69
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	70 <TD VALIGN=TOP NOWRAP WIDTH="50%">
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	71 <A HREF="#Nonterminal">Nonterminal Token</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	72 <A HREF="#NullProduction">Null Production</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	73 <A HREF="#ParameterAssignment">Parameter Assignment</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	74 <A HREF="#Parser">Parser</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	75 <A HREF="#ParserGenerator">Parser Generator</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	76 <A HREF="#ParserStateStack">Parser State Stack</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	77 <A HREF="#ParserValueStack">Parser Value Stack</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	78 <A HREF="#ParsingEngine">Parsing Engine</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	79 <A HREF="#SetPartition">Partition</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	80 <A HREF="#Precedence">Precedence</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	81 <A HREF="#Production">Production</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	82 <A HREF="#ReduceAction">Reduce Action</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	83 <A HREF="#ReduceReduce">Reduce-Reduce Conflict</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	84 <A HREF="#ReducingToken">Reducing Token</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	85 <A HREF="#ReductionProcedure">Reduction Procedure</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	86 <A HREF="#ReductionToken">Reduction Token</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	87 <A HREF="#Resynchronization">Resynchronization</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	88 <A HREF="#RuleElement">Rule Element</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	89 <A HREF="#SemanticAction">Semantic Action</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	90 <A HREF="#SemanticValue">Semantic Value</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	91 <A HREF="#SemanticallyDetermined">Semantically Determined Production</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	92 <A HREF="#SetExpression">Set Expression</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	93 <A HREF="#ShiftAction">Shift Action</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	94 <A HREF="#ShiftReduce">Shift-Reduce Conflict</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	95 <A HREF="#SyntaxDirectedParsing">Syntax Directed Parsing</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	96 <A HREF="#Terminal">Terminal Token</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	97 <A HREF="#Token">Token</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	98 <A HREF="#UnaryOperator">Unary Operator</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	99 <A HREF="#SetUnion">Union</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	100 <A HREF="#VirtualProduction">Virtual Production</A><BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	101
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	102 </TD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	103
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	104 </TABLE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	105
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	106 <HR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	107
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	108
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	109
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	110 <DL>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	111 <DT><B><A NAME="ParserAction">Action</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	112 <DD>A "parser action" is one of the basic executable elements of a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	113 <A HREF="#ParsingEngine">parsing engine</A>. In a traditional parsing engine
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	114 there are four actions: the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	115 <A HREF="#ShiftAction">shift action</A>, the <A HREF="#ReduceAction">reduce
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	116 action</A>, the <A HREF="#AcceptAction">accept action</A>, and the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	117 <A HREF="#ErrorAction">error action</A>. The parsing engines which AnaGram
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	118 generates use a substantially greater number of actions, in order to provide
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	119 certain short cuts in the interest of greater speed and greater compactness of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	120 the tables which control the action of the parsing engine.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	121 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	122 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	123
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	124 <DT><B><A NAME="AcceptAction">Accept Action</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	125 <DD> The accept <A HREF="#ParserAction">action</A> is one of the four actions
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	126 of a traditional <A HREF="#ParsingEngine">parsing engine</A>. The accept action
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	127 is performed when the <A HREF="#Parser">parser</A> has succeeded in identifying
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	128 the <A HREF="#GrammarToken">goal token</A> for the <A HREF="#Grammar">grammar</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	129 When the parser executes the accept action, it returns to the calling program.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	130 The accept action is thus the last action of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	131 the parsing engine and occurs only once for each successful execution
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	132 of the parser.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	133
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	134 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	135 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	136
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	137 <DT><B><A NAME="Associativity">Associativity</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	138 <DD> This is a term used to describe <A HREF="#BinaryOperator">binary
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	139 operators </A>. It describes how you interpret a sequence of operations which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	140 all involve the same operator. Consider a - b - c, for instance. Here the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	141 convention is that we subtract b from a, and then c from the difference. We say
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	142 that subtraction is <B>left associative</B>, since if there is a sequence of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	143 subtraction operations, the leftmost one is to be performed first. As a second
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	144 example, consider exponentiation. FORTRAN uses ** as an operator to indicate
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	145 exponentiation. In order to conform as closely as possible to ordinary
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	146 mathematical notation, the expression abc is interpreted to mean that first
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	147 b is raised to the power c, and then the resultant value is used as the power to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	148 which a is raised. We say that exponentiation is <B>right associative</B> since the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	149 rightmost of a sequence of exponentiation operations is to be performed first.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	150 If a programming language does not allow for unparenthesized sequences of a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	151 particular operator, the operator is said to be non-associative.<P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	152 Another way to view left and right associativity is as implied parenthesization.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	153 Left associative operators are parenthesized from the left. Right associative
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	154 operators are parenthesized from the right. Thus a - b - c = ((a-b) - c) and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	155 abc = (a(bc))</P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	156 AnaGram offers two ways to specify associativity of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	157 <A HREF="#BinaryOperator">binary operators</A>. The first
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	158 way is to use conventional <A HREF="#BNF">Backus-Naur Form</A> syntax
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	159 descriptions. You would userecursion to describe both subtraction and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	160 exponentiation. Subtraction, since it is left associative, uses left recursion,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	161 and exponentiation, being right associative, uses right recursion. Thus</P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	162 </P><PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	163 difference -> value \| difference, '-', value
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	164 exponential -> value \| value, "**", exponential
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	165 </PRE> could be used to describe differences and exponents.<P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	166 The second way to specify associativity is to use an ambiguous <A HREF="#Grammar">grammar</A> and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	167 precedence declarations. (See Chapter 9, AnaGram User's Guide.)</P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	168 </P></DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	169
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	170 <DT><B><A NAME="Backtracking">Backtracking</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	171 <DD> In order to make parse tables more compact and <A HREF="#Parser">parsers</A> faster, it is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	172 common to use <A HREF="#DefaultReduction">default reductions</A>. In case of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	173 error, it is necessary to undo default reductions before diagnostics can be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	174 properly determined. In AnaGram, this undo operation is called backtracking.<P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	175
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	176 </P></DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	177
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	178 <DT><B><A NAME="BNF">Backus-Naur Form</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	179 <DD> Backus-Naur Form, or BNF, is a conventional notation for describing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	180 <A HREF="#ContextFreeGrammar">context free grammars</A>. AnaGram uses an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	181 extended notation for <A HREF="#Grammar">grammars</A>, which, except for
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	182 <A HREF="#SemanticallyDetermined">semantically determined
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	183 productions</A>, can be shown to be equivalent to BNF. The term "BNF" is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	184 often used colloquially to refer to a grammar specification.<P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	185 AnaGram's syntax specification language differs from BNF in the following
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	186 respects:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	187 </P><OL>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	188 <LI>In conventional BNF, a symbol not enclosed in angle brackets (< >) is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	189 taken to represent itself literally. In AnaGram, literal character
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	190 representations must be enclosed in single quotes and literal strings within
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	191 double quotes.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	192 </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	193 <LI>In BNF, the right side of a <A HREF="#Production">production</A> is simply a list of symbols without
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	194 any delimiters or punctuation. AnaGram requires that the <A HREF="#RuleElement">rule elements</A> which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	195 make up a <A HREF="#GrammarRule">grammar rule</A>, or right side, be joined by commas.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	196 </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	197 <LI>BNF makes no provision for identifying <A HREF="#ReductionProcedure">reduction procedures</A> or their
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	198 arguments. AnaGram provides both reduction procedures, introduced by an "="
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	199 at the end of the production, and named arguments, introduced by a ":"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	200 at the end of any <A HREF="#Token">token</A> on the right side of the production.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	201 </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	202 <LI>AnaGram allows <A HREF="#VirtualProduction">virtual productions</A> to be used freely.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	203 </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	204 <LI>BNF is "pure" in that if you wish to define a <A HREF="#Nonterminal">nonterminal token</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	205 called "digit" to represent the digits from zero to nine, you must
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	206 provide ten explicit productions to define it. AnaGram treats the concept of <A HREF="#Terminal">"terminal
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	207 token"</A> as used in language theory as an abstraction, and interposes
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	208 <A HREF="#CharacterSets">character set</A> functionality between actual character input and the terminal
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	209 tokens of BNF. You can define digit to be the character range '0-9', for
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	210 instance, and AnaGram will determine and define precisely the minimum number of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	211 productions necessary, taking into account any other usage of the characters
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	212 '0-9' in your grammar. This makes your grammar more compact, more manageable,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	213 and easier to modify.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	214 </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	215 <LI>AnaGram allows for <A HREF="#SemanticallyDetermined">
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	216 semantically determined productions</A>, which provide a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	217 significant mechanism for melding semantic analysis with syntactic
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	218 analysis.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	219
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	220 </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	221 </OL>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	222 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	223
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	224 <DT><B><A NAME="BinaryOperator">Binary operator</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	225 <DD> A binary operator is an operator that works on two operands to create a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	226 result. It is often written between its operands and is sometimes called an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	227 infix operator. In ordinary programming languages "+" and "-"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	228 are binary operators.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	229 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	230 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	231
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	232 <DT><B><A NAME="Binding">Binding</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	233 <DD> Most programming languages, rather than executing arithmetic operators in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	234 simple left to right order, conform to the traditional conventions of ordinary
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	235 algebra, which dictate that, except where parenthesis indicate otherwise,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	236 exponentiation is done before multiplication, multiplication before addition,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	237 and addition before comparison. One says that exponentiation is "more
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	238 tightly binding" than multiplication, multiplication is more tightly
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	239 binding than addition, and so on. The sense of the word here is that the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	240 operator binds together its operands into a single entity. An operand which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	241 falls between two different operators is "bound" by the more tightly
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	242 binding operator. An operator that is more tightly binding than another is also
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	243 said to have higher <A HREF="#Precedence">precedence</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	244 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	245 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	246
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	247 <DT><B><A NAME="CharacterSets">Character sets</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	248 <DD> One of the traditional problems with syntax directed programming is that
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	249 caused by the fact that most formal language specifications have productions of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	250 the form:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	251 <PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	252 letter -> a \| b \| c \| d ... \| z
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	253 </PRE> Since the letters are not often distinguished in the <A HREF = "#Grammar">grammar</A>, this large
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	254 number of essentially identical <A HREF="#Production">productions</A> causes a correspondingly large
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	255 number of states in the <A HREF="#Parser">parser</A>. This problem is often attacked by using a<A
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	256 HREF="#LexicalScanner"> "lexical scanner"</A> which simply specifies
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	257 a "letter token" whose value indicates precisely which letter is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	258 intended. This works fine as long as there is nothing in the grammar which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	259 distinguishes any letter at all. If there is, and there is usually some special
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	260 use of h, x, q, o, e, or even a-f, the situation gets more complicated. Often the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	261 result is to abandon the use of syntax directed programming for elemental units
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	262 of the language and use a more complex lexical scanner which identifies names,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	263 numbers, key words and operators. Such lexical scanners are often built using
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	264 conventional programming languages or simple pattern recognizing languages such
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	265 as LEX.<P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	266 AnaGram avoids this problem by incorporation the notion of character set into
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	267 its input specifications. Briefly, the way it works is the following: You
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	268 specify the set of characters which make up any ostensibly <A HREF="#Terminal">terminal token</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	269 AnaGram then analyzes the overlaps among these definitions and creates a minimal
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	270 set of <A HREF="#Token">tokens</A> which match your specifications exactly. For instance, suppose you
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	271 have the following definitions:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	272 </P><PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	273 letter = 'a-z' + 'A-Z'
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	274 hex digit = '0-9' + 'a-f' + 'A-F'
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	275 </PRE> AnaGram will define a token for letter which has two productions:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	276 <PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	277 letter -> 'a-f' + 'A-F' \| 'g-z' + 'G-Z'
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	278 </PRE> With this technique, you have the freedom to specify your grammar in the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	279 easiest possible manner, without the penalty of an absurdly large, slow parser.<P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	280 Character sets may be specified in terms of ranges of characters, as in the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	281 above example, as <A HREF="#SetUnion">unions</A>, denoted by "+", as
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	282 <A HREF="#SetIntersection">intersections</A>, denoted by "&", as
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	283 <A HREF="#SetDifference">differences,</A> denoted by "-", and as
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	284 <A HREF="#SetComplement">complements</A>, using "~". You may also
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	285 specify a set consisting of a single character either with a literal character
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	286 or with a numeric specification. If you specify a character numerically, you may
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	287 use either decimal, octal or hexadecimal notation, as in C.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	288 </P><P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	289 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	290
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	291 <DT><B><A NAME="Universe">Character Universe</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	292 <DD> In ordinary set theory, the "universe" is the set of all
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	293 entities which may be elements of a set. It must be defined so that the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	294 complement of a set can mean something unambiguous. In AnaGram, the character
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	295 universe normally comprises the ascii characters and the IBM extended character
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	296 set, that is, all characters in the range from 0 through 255. If, however, you
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	297 have defined input characters outside this range, the character universe will be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	298 extended to the least character you have used and to the greatest character you
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	299 have used in your <A HREF = "#Grammar">grammar</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	300 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	301 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	302
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	303 <DT><B><A NAME="CharacteristicRule">Characteristic Rule</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	304 <DD> Each parser state is characterized by a particular set of <A HREF="#GrammarRule">grammar rules</A>,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	305 and for each such rule, a marked token which is the next <A HREF="#Token">token</A> expected. These
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	306 rules are called the characteristic rules for the state. In the course of doing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	307 <A HREF="#GrammarAnalysis">grammar analysis</A>, AnaGram determines the characteristic rules for each parser
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	308 state. After analyzing your grammar, you may inspect the State Definition Table
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	309 to see the characteristic rules for any state in your <A HREF="#Parser">parser</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	310 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	311 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	312
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	313 <DT><B><A NAME="CharacteristicToken">Characteristic Token</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	314 <DD> Every state in a <A HREF="#Parser">parser</A>, except state zero, can be characterized by the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	315 one, unique <A HREF="#Token">token</A> which causes a jump to that state. That token is called the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	316 characteristic token of the state, because to get to that parser state you must
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	317 have just seen precisely that token in the input. Note that several states could
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	318 have the same characteristic token.<P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	319 When you have a list of states, such as is given by the parser state stack, it
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	320 is equivalent to a list of characteristic tokens. This list of tokens is the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	321 list of tokens that have been recognized so far by the parser. Some of these
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	322 tokens, of course, may be <A HREF="#Nonterminal">nonterminal tokens</A> and may thus represent the result
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	323 of reducing a sequence of previously recognized tokens.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	324 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	325 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	326 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	327
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	328 <DT><B><A NAME="SetComplement">Complement of a set</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	329 <DD> In set theory, the complement of a set, S, is the collection of all
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	330 elements of the <A HREF="#Universe">character universe</A> which are not elements of S. Using AnaGram's
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	331 notation, the complement of S is written ~S. The complement operator has higher
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	332 <A HREF="#Precedence">precedence</A> than the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	333 <A HREF="#SetDifference">difference</A>, <A HREF="#SetIntersection">intersection</A>, or <A HREF="#SetUnion">union</A> operators.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	334 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	335 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	336
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	337 <DT><B><A NAME="CompletedRule">Completed Rule</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	338 <DD> A "completed rule" is a <A HREF="#CharacteristicRule">characteristic rule</A> whose index is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	339 pointing beyond the last <A HREF="#RuleElement">rule element</A>. In other words, it has been completely
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	340 matched and will be <A HREF="#ReduceAction">reduced</A> by the next input.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	341 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	342 If a state has more than one completed rule, the decision as to which to reduce
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	343 is made based on the next input <A HREF="#Token">token</A>. If there is only one completed rule in a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	344 state, it will be reduced by default unless the default reductions switch has
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	345 been reset, i.e., turned off.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	346 </P></DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	347 <DT><B><A NAME="Conflict">Conflict</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	348 <DD> Conflicts arise during a <A HREF="#GrammarAnalysis">grammar analysis</A> when AnaGram cannot determine
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	349 how to treat a given input <A HREF="#Token">token</A>. There are two sorts of conflicts: <A HREF="#ShiftReduce">shift-reduce
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	350 conflicts</A> and <A HREF="#ReduceReduce">reduce-reduce conflicts</A>. Conflicts may arise either because the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	351 <A HREF = "#Grammar">grammar</A> is inherently ambiguous, or simply because the grammar analyzer cannot
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	352 look far enough ahead to resolve the conflict. In the latter case, it is often
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	353 possible to rewrite the grammar in such a way as to eliminate the conflict. <A HREF="#NullProduction">Null
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	354 productions</A> are a common source of conflict.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	355 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	356 There are a number of ways to deal with conflicts. If you understand the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	357 conflict well, you may simply choose to ignore it. When AnaGram encounters a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	358 shift-reduce conflict while building parse tables it resolves it by choosing the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	359 <A HREF="#ShiftAction">shift action</A>. When AnaGram encounters a reduce-reduce conflict while building
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	360 parse tables, it resolves it by selecting the <A HREF="#GrammarRule">grammar rule</A> which occurred first
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	361 in the grammar.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	362 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	363 A second way to deal with conflicts is to set operator <A HREF="#Precedence">precedence</A> parameters. If
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	364 you set these parameters, AnaGram will use them preferentially to resolve
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	365 conflicts. Any conflicts so resolved will be listed in the Resolved Conflicts
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	366 window.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	367 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	368 A third way to resolve a conflict is to declare some tokens as sticky or as
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	369 subgrammars. This is particularly useful for <A HREF="#Production">productions</A> whose sole purpose is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	370 to skip over uninteresting input.</P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	371 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	372 The fourth way to deal with conflicts is to rewrite the grammar to eliminate
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	373 them. Many people prefer this approach since it yields the highest level of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	374 confidence in the resulting program.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	375 </P></DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	376 <DT><B><A NAME="ContextFreeGrammar">Context Free Grammars</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	377 <DD> Context free grammars are <A HREF = "#Grammar">grammars</A> wherein the definition of a grammar
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	378 unit, or <A HREF="#Nonterminal">nonterminal token</A>, does not depend on the context in which the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	379 nonterminal is used. That means that if you define "widget" in a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	380 certain way, that definition is valid in all contexts in which "widget"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	381 might occur. Context free grammars can be represented in <A HREF="#BNF">Backus-Naur Form</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	382 AnaGram's syntax specification language has no facility for representing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	383 grammars which are not context free.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	384 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	385 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	386 <DT><B><A NAME="DefaultReduction">Default reductions</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	387 <DD> A "default reduction" is a parser action which may be used in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	388 your <A HREF="#Parser">parser</A> in any state which has precisely one <A HREF="#CompletedRule">completed rule</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	389 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	390 If a given parser state has, among its <A HREF="#CharacteristicRule">characteristic rules</A>, exactly one
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	391 completed rule, it is usually faster to reduce it on any input than to check
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	392 specifically for correct input before reducing it. The only time this default
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	393 reduction causes trouble is in the event of a syntax error. In this situation
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	394 you may get an erroneous reduction. Normally when you are parsing a file, this
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	395 is inconsequential because you are not going to continue performing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	396 <A HREF="#SemanticAction">semantic actions</A> in the presence of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	397 errors. But, if you are using your parser to handle real-time
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	398 interactive input, you have to be able to continue semantic
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	399 processing after notifying your user that he has entered erroneous
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	400 input. In this case you would want default reductions to have been
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	401 turned off so that <A HREF="#Production">production</A>s are reduced
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	402 only when there is correct input.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	403
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	404 </P></DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	405
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	406 <DT><B><A NAME="SetDifference">Difference of two sets</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	407 <DD> In set theory, the difference of two sets, A and B, is defined to be the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	408 set of all elements of A that are not elements of B. In an AnaGram syntax file,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	409 you represent the difference of two <A HREF="#CharacterSets">character sets</A> by using the "-"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	410 operator. Thus the difference of A and B is A - B. The difference operator is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	411 <A HREF="#Associativity">left associative</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	412 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	413 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	414
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	415 <DT><B><A NAME="ErrorAction">Error Action</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	416 <DD> The error action is one of the four <A HREF="#ParserAction">actions</A> of a traditional <A HREF="#ParsingEngine">parsing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	417 engine</A>. The error action is performed when the <A HREF="#Parser">parser</A> has encountered an input
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	418 <A HREF="#Token">token</A> which is not admissible in the current state. The further behavior of a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	419 traditional parser is undefined.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	420 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	421 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	422
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	423 <DT><B><A NAME="EventDriven">Event Driven Parser</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	424 <DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	425 An <I>event driven</I> <A HREF="#Parser">parser</A> is one in which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	426 the relationship between the host program and the parser is turned
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	427 inside out. In a conventional parser, the host program calls the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	428 parser, the parser analyzes the complete input text and returns to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	429 the host program only when it has finished with the entire input.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	430 <P>In an event driven parser, the parser does not read its input
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	431 directly from a file or from memory. Instead, the host program, after
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	432 initializing the parser, calls it once for each input token. Each
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	433 time the parser is called, it updates its state
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	434 appropriately, calls any <A HREF="#ReductionProcedure">reduction
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	435 procedures</A> that need to be called and finally when it needs more
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	436 input, returns to the host program. The effect is that parsing can
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	437 occur in parallel with other processing performed by the host
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	438 program. This technique is especially useful in situations where the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	439 token stream to be parsed is developed on the fly, as when using <A
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	440 HREF="#LexicalScanner">lexical scanners</A>, for instance.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	441 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	442 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	443
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	444
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	445 <DT><B><A NAME="ExpansionRule">Expansion Rule</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	446 <DD> In analyzing a <A HREF = "#Grammar">grammar</A>, we are often interested in the full range of input
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	447 that can be expected at a certain point. The expansion of a <A HREF="#Token">token</A> or state shows
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	448 us all the expected input. An expansion yields a set of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	449 <A HREF="#MarkedRule">marked rules</A>. Looking
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	450 at the marked token shows us what input to expect.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	451 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	452 The set of expansion rules of a <A HREF="#Nonterminal">nonterminal token</A> shows all the expected input
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	453 that can occur whenever the token appears in the grammar. The set consists of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	454 all the <A HREF="#GrammarRule">grammar rules</A> produced by the token, plus all the rules produced by the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	455 first token of any rule in the set. The marked tokens for the expansion rules of a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	456 token are always the first element in the rule.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	457 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	458 The expansion of a state consists of its
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	459 <A HREF="#CharacteristicRule">characteristic rules</A> plus the expansion
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	460 rules of the marked token in each characteristic rule.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	461 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	462 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	463
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	464
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	465 <DT><B><A NAME="Grammar">Grammar</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	466 <DD> Traditionally, a grammar is a set of <A HREF="#Production">productions</A> which taken together
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	467 specify precisely a set of acceptable input sequences in terms of an abstract
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	468 set of <A HREF="#Terminal">terminal tokens</A>. The set of acceptable input sequences is often called
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	469 the "language" defined by the grammar.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	470 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	471 In AnaGram, the term grammar also includes configuration segments, definitions
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	472 of <A HREF="#CharacterSets">character sets</A>, <A HREF="#VirtualProduction">virtual productions</A>, etc. that augment the collection of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	473 productions. A grammar is often called a "syntax", and the <A HREF="#GrammarRule">rules of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	474 the grammar</A> are often called syntactic rules.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	475 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	476 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	477 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	478
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	479 <DT><B><A NAME="GrammarAnalysis">Grammar Analysis</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	480 <DD> The major function of AnaGram is the analysis of <A HREF = "#ContextFreeGrammar">context free grammars</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	481 written in a particular variant of <A HREF="#BNF">Backus-Naur Form</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	482 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	483 The analysis of a <A HREF="#Grammar">grammar</A> proceeds in four stages. In the first, the input
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	484 grammar is analyzed and a number of tables are built which describe all of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	485 <A HREF="#Production">productions</A> and components of the grammar.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	486 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	487 In the second stage, AnaGram analyzes all of the <A HREF="#CharacterSets">character sets</A> defined in the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	488 grammar, and where necessary, defines auxiliary <A HREF="#Token">tokens</A> and productions.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	489 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	490 In the third stage, AnaGram identifies all of the states of the <A HREF="#Parser">parser</A> and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	491 builds the go-to table for the parser.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	492 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	493 In the fourth stage, Anagram identifies <A HREF="#ReductionToken">reduction tokens</A> for each completed
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	494 <A HREF="#GrammarRule">grammar rule</A> in each state and checks for <A HREF="#Conflict">conflicts</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	495 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	496 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	497 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	498
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	499 <DT><B><A NAME="GrammarRule">Grammar Rule</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	500 <DD> A "grammar rule" is the right side of a <A HREF="#Production">production</A>. It consists
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	501 of a sequence of <A HREF="#RuleElement">rule elements</A>. Each rule element identifies some <A HREF="#Token">token</A>, which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	502 can be either a <A HREF="#Terminal">terminal token</A> or <A HREF="#Nonterminal">nonterminal token</A>. It is "matched"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	503 by a corresponding sequence of tokens in the input stream to the <A HREF="#Parser">parser</A>. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	504 left side of the production identifies one or more nonterminal tokens, or
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	505 <A HREF="#ReductionToken">reduction tokens</A>, to which the rule reduces when matched. If there is more than
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	506 one reduction token, there should be a <A HREF="#ReductionProcedure">reduction procedure</A> to make the choice.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	507 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	508 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	509
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	510 <DT><B><A NAME="GrammarToken">Grammar Token</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	511 <DD> The grammar <A HREF="#Token">token</A> is the token which represents the "top level"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	512 in your grammar. Some people refer to it as the "goal" or "goal
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	513 token" and others as the "start token". Whatever it is called, it
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	514 is the single token which describes the complete input to your <A HREF="#Parser">parser</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	515 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	516 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	517
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	518 <DT><B><A NAME="SetIntersection">Intersection</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	519 <DD> In set theory, the intersection of two sets, A and B, is defined to be the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	520 set of all elements of A which are also elements of B. In an AnaGram syntax
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	521 file, the intersection of two <A HREF="#CharacterSets">character sets</A> is represented with the "&"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	522 operator. The intersection operator has lower <A HREF="#Precedence">precedence</A> than the complement
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	523 operator, but higher precedence than the <A HREF="#SetUnion">union</A> and <A HREF="#SetDifference">difference</A> operators. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	524 intersection operator is <A HREF="#Associativity">left associative</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	525 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	526 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	527
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	528 <DT><B><A NAME="LALRParsing">LALR parsing</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	529 <DD> LALR, or "lookahead LR" parsing, a slightly less powerful
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	530 variant of <A HREF="#LRParsing">LR parsing</A>, produces much smaller parsing tables. Thus an LALR
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	531 <A HREF="#Parser">parser</A> has very significant advantages in size over its LR counterpart. It is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	532 possible to construct <A HREF = "#Grammar">grammar</A>s which can be parsed by an LR parser but cannot be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	533 parsed by an LALR parser. That is, the LALR parser will find these grammars to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	534 be ambiguous and the LR parser will not. In practice, however, such grammars
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	535 seem to be rare and the ambiguities can usually be eliminated by minor revisions.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	536 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	537 AnaGram generates LALR parsers and, in addition, uses LALR parsing to interpret
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	538 syntax files.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	539 </P><P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	540 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	541
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	542 <DT><B><A NAME="LexicalScanner">Lexical Scanner</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	543 <DD> A lexical scanner is a program or procedure used as a preprocessor for a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	544 <A HREF="#Parser">parser</A>. It scans input characters and lumps them together into <A HREF="#Token">tokens</A>. Many
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	545 systems for generating parsers, most notably YACC, can scarcely be used without
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	546 a lexical scanner.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	547 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	548 AnaGram, although it can support the use of a lexical scanner, does not need a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	549 lexical scanner for most practical problems. AnaGram avoids the need for a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	550 lexical scanner by using <A HREF="#CharacterSets">character sets</A> and disregard and lexeme statements.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	551 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	552 If your problem does in fact need a lexical scanner, you can use AnaGram itself
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	553 to write it, so you don't need to know different languages for the scanner and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	554 for the parser.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	555 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	556 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	557 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	558
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	559 <DT><B><A NAME="Lookahead">Lookahead Token</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	560 <DD> The current input <A HREF="#Token">token</A> to a <A HREF="#Parser">parser</A> is often called the "lookahead"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	561 token. In many situations, it is not shifted into the input buffer immediately,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	562 but acts like a catalyst to cause a number of rules to be reduced before it is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	563 eventually shifted in.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	564 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	565 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	566
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	567 <DT><B><A NAME="LRParsing">LR Parsing</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	568 <DD> An LR(k) <A HREF="#Parser">parser</A> is a type of deterministic bottom-up shift-reduce parser
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	569 using at most k lookahead symbols to determine its next <A HREF="#ParserAction">action</A> at any point in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	570 the parse. If (k) is omitted, then k is assumed to be 1. Discussion of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	571 technical details of LR(k) parsing is beyond the scope of this manual. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	572 interested reader may consult any of a variety of works covering the subject.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	573 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	574 AnaGram produces parsers which employ a variant of LR parsing known as LALR
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	575 parsing. It is not necessary to understand the details of LR and LALR parsing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	576 theory in order to use AnaGram.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	577 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	578 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	579 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	580
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	581 <DT><B><A NAME="MarkedRule">Marked Rule</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	582 <DD> A "marked rule" is a <A HREF="#GrammarRule">grammar rule</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	583 together with a "marked token"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	584 that indicates how much of the rule has already been matched and what input
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	585 should be expected, starting with the marked token, if the remainder of the rule is to be matched. Each <A HREF="#Parser">parser</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	586 state is defined by a small number of <A HREF="#CharacteristicRule">characteristic rules</A> which indicate what
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	587 matches have already been made and what input can be expected. Note that when a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	588 state has more than one characteristic rule, any two characteristic rules with
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	589 the same number of <A HREF="#Token">tokens</A> to the left of the marked token
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	590 match identically up to the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	591 marked token. If one rule has fewer tokens to the left than the other, all of its tokens
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	592 preceding the marked token match the corresponding tokens of the longer rule
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	593 exactly.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	594 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	595 When marked rules are displayed in AnaGram windows, the marked token is displayed in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	596 a distinctive font which the developer can select. The default is italic.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	597 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	598 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	599 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	600
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	601 <DT><B><A NAME="NonAssociative">Non-associative</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	602 <DD> A <A HREF="#BinaryOperator">binary operator</A>, say #, is said to be non-associative if the sequence x
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	603 # y # z is not permissible. If this sequence is to be interpreted as (x#y)#z,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	604 the operator is said to be <B>left associative</B>. If the sequence is to be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	605 interpreted as x#(y#z), the operator is said to be <B>right associative</B>. (See
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	606 <A HREF="#Associativity">associativity</A>.)
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	607 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	608 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	609
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	610 <DT><B><A NAME="Nonterminal">Nonterminal Token</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	611 <DD> A "nonterminal token" is a <A HREF="#Token">token</A> which results from reducing the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	612 sequence of tokens which match a <A HREF="#GrammarRule">grammar rule</A> and replacing them with the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	613 appropriate <A HREF="#ReductionToken">reduction token</A>. Nonterminal tokens are to be distinguished from
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	614 <A HREF="#Terminal">terminal tokens</A> or input tokens.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	615 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	616 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	617
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	618 <DT><B><A NAME="NullProduction">Null Production</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	619 <DD> A "null production" is one that has no <A HREF="#Token">tokens</A> on the right side
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	620 whatsoever. Null <A HREF="#Production">production</A>s essentially are identified by the first following
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	621 input token. Null productions are extremely convenient syntactic elements when
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	622 you wish to make some input optional. For example, suppose that you wish to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	623 allow an optional semicolon at some point in your <A HREF = "#Grammar">grammar</A>. You could write the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	624 following pair of productions:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	625 <PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	626 optional semicolon -> \| ';'
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	627 </PRE> Note that a null production can never follow a '\|'. The above could also
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	628 be written on multiple lines thus:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	629 <PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	630 optional semicolon
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	631 ->
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	632 -> ';'
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	633 </PRE> You can always rewrite your grammar to eliminate null productions if you
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	634 wish, but you usually pay a price in conciseness and clarity. Sometimes,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	635 however, it is necessary to do such a rewrite in order to avoid <A HREF="#Conflict">conflicts</A>, to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	636 which null productions are especially prone.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	637 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	638 If you have a null production with no <A HREF="#ReductionProcedure">reduction procedure</A> specified, your <A HREF="#Parser">parser</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	639 will automatically assign the value zero to the <A HREF="#ReductionToken">reduction token</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	640 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	641 Null productions can be generated by <A HREF="#VirtualProduction">virtual productions</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	642 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	643 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	644 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	645
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	646 <DT><B><A NAME="ParameterAssignment">Parameter Assignment</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	647
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	648 <DD>In any <A HREF="#GrammarRule"> grammar rule</A>, the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	649 <A HREF="#SemanticValue">semantic value</A> of any
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	650 <A HREF="#RuleElement">rule element</A> may be passed to a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	651 <A HREF="#ReductionProcedure">reduction procedure</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	652 by means of a parameter assignment. In AnaGram this is particularly
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	653 convenient since you can use an ordinary variable name for the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	654 parameter. Simply follow the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	655 rule element with a colon and a C variable name. The C
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	656 variable name can then be used in the reduction
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	657 procedure to reference the semantic value of the token
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	658 it is attached to. AnaGram will automatically provide
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	659 necessary declarations.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	660
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	661 Here are some examples of rule elements with parameter
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	662 assignments:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	663 <PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	664 '0-9':d
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	665 integer:n
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	666 expression:x
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	667 declaration : declaration_descriptor
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	668 </PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	669 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	670
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	671 <DT><B><A NAME="Parser">Parser</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	672 <DD> A parser is a program, or more likely a procedure within a program, which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	673 scans a sequence of input characters or input <A HREF="#Token">tokens</A> and accumulates them in an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	674 input buffer or stack as determined by a set of <A HREF="#Production">productions</A> which constitute a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	675 <A HREF = "#Grammar">grammar</A>. When the parser discovers a sequence of tokens as defined by a <A HREF="#GrammarRule">grammar
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	676 rule</A>, or right side of a production, it "reduces" the sequence to a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	677 single <A HREF="#ReductionToken">reduction token</A> as defined by the left side of the <A HREF="#GrammarRule">grammar rule</A>. This
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	678 <A HREF="#Nonterminal">nonterminal token</A> now replaces the tokens which matched the grammar rule and the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	679 search for matches continues. If an input token is encountered which will not
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	680 yield a match for any rule, it is considered a syntax error and some kind of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	681 error recovery may be required to continue. If a match, or reduction action,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	682 yields the grammar token, sometimes called the goal token or start token, the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	683 parser deems its work complete and returns to whatever procedure may have called
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	684 it.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	685 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	686 Tokens may have <A HREF="#SemanticValue">semantic values</A>. If the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	687 input values configuration switch is on, your parser will expect
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	688 semantic values to be provided by the input process along with the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	689 token identification code. If the input values switch is off, your
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	690 parser will take the ascii value of the input character, that is, the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	691 actual input code, as the value of the character. When the parser <A
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	692 HREF="#ReduceAction">reduces</A> a <A
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	693 HREF="#Production">production</A>, it can call a <A
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	694 HREF="#ReductionProcedure">reduction procedure</A> or <A
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	695 HREF="#SemanticAction">semantic action</A> to analyze the values of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	696 the constituent tokens. This reduction procedure can then return a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	697 value which characterizes the reduced token.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	698 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	699 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	700 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	701
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	702 <DT><B><A NAME="ParserGenerator">Parser Generator</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	703 <DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	704 A parser generator, such as AnaGram, is a program that
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	705 converts a <A HREF="#Grammar">grammar</A>, a rule-based description of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	706 input to a program, into a conventional, procedural
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	707 module called a <A HREF="#Parser">parser</A>. The parsers AnaGram generates
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	708 are simple C modules which can be compiled on almost
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	709 any platform. AnaGram parsers are also compatible with
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	710 C++.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	711 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	712 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	713
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	714 <DT><B><A NAME="ParserStateStack">Parser State Stack</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	715 <DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	716 The parser state stack is a stack maintained by an AnaGram
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	717 parser and which is an integral part of the parsing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	718 process. At any point in the parse of your input
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	719 stream, the parser state stack provides a list of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	720 states which were traversed in order to arrive at the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	721 current state.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	722
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	723 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	724 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	725
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	726
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	727 <DT><B><A NAME="ParserValueStack">Parser Value Stack</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	728 <DD>In parallel with the <A HREF="#ParserStateStack">parser state stack</A>,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	729 an AnaGram <A HREF="#Parser"> parser</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	730 maintains a <I>value stack</I> each entry of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	731 which corresponds to the <A HREF="#SemanticValue">semantic value</A> of the token
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	732 identified at that state. Since the semantic values of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	733 different tokens might well have different data types,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	734 AnaGram gives you the opportunity, in your syntax
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	735 file, to define the data type for any token. AnaGram
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	736 then builds a typedef statement creating a data type
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	737 which is a union of the all the types you have defined.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	738 AnaGram creates the name for this data type by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	739 appending "_vs_type" to the name of the parser. AnaGram uses
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	740 this data type to define the value stack.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	741 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	742 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	743
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	744
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	745 <DT><B><A NAME="ParsingEngine">Parsing Engine</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	746 <DD> A <A HREF="#Parser">parser</A> consists of three basic components: A set of syntax tables, a set
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	747 of <A HREF="#ReductionProcedure">reduction procedures</A> and a parsing engine. The parsing engine is the body of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	748 code that interprets the parsing table, invokes input functions, and calls the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	749 reduction procedures. The Build Parser command configures a parsing engine
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	750 according to the implicit requirements of the syntax specification and according
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	751 to the explicit values of the configuration parameters.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	752 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	753 The parsing engine itself is a simple automaton, characterized by a set of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	754 states and a set of inputs. The inputs are the <A HREF="#Token">tokens</A> of your <A HREF = "#Grammar">grammar</A>. Each
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	755 state is represented by a list of tokens which are admissible in that state and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	756 for each token an <A HREF="#ParserAction">action</A> to perform and a parameter which further defines the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	757 action. In a traditional <A HREF="#LALRParsing">LALR parser</A>, there are only four <A HREF="#ParserAction">actions</A>: the <A HREF="#ShiftAction">shift
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	758 action</A>, the <A HREF="#ReduceAction">reduce action</A>, the <A HREF="#AcceptAction">accept action</A> and the <A HREF="#ErrorAction">error action</A>. AnaGram, in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	759 doing its <A HREF="#GrammarAnalysis">grammar analysis</A>, identifies a number of special cases, and creates a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	760 number of extra actions which make for faster processing, but which can be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	761 represented as combinations of these primitive actions.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	762 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	763 When a shift action is performed, the current state number is pushed onto the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	764 parser state stack and the new state number is determined by the current state
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	765 number and the current lookahead token. Different tokens cause different new
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	766 states.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	767 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	768 When a reduce action is performed, the length of the rule being reduced is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	769 subtracted from the parser stack index and the new state number is read from the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	770 top of the parser state stack. The <A HREF="#ReductionToken">reduction token</A> for the rule being reduced is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	771 then used as an input token.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	772 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	773 Each state in the grammar, with the exception of state zero, has a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	774 <A HREF="#CharacteristicToken">characteristic token</A> which must have been recognized in order to jump to that
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	775 state. Therefore, the parser state stack, which is essentially a list of state
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	776 numbers, can also be thought of as a list of token numbers. This is the list of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	777 tokens that have been seen so far in the parse of your input stream. Some of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	778 these tokens, of course, may be <A HREF="#Nonterminal">nonterminal tokens</A> which have resulted from
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	779 reducing other sequences of tokens.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	780 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	781 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	782 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	783
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	784 <DT><B><A NAME="SetPartition">Partition</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	785 <DD> If you use <A HREF="#CharacterSets">character sets</A> in your <A HREF = "#Grammar">grammar</A>, AnaGram will compute a "partition"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	786 of the <A HREF="#Universe">character universe</A>. This partition is a collection of non-overlapping
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	787 character sets such that every one of the sets you have defined can be written
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	788 as a <A HREF="#SetUnion">union</A> of partition sets. Each partition set is identified by a unique
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	789 reference number called the partition set number.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	790 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	791 Each partition set is assigned a unique <A HREF="#Token">token</A>. If one of your character sets
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	792 requires more than one partition set to represent it, AnaGram will create
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	793 appropriate <A HREF="#Production">productions</A> and add them to your grammar so your <A HREF="#Parser">parser</A> can make the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	794 necessary distinctions.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	795 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	796 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	797 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	798
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	799 <DT><B><A NAME="Precedence">Precedence</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	800 <DD> "Precedence" is an attribute of <A HREF="#BinaryOperator">binary operators</A> and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	801 <A HREF = "#UnaryOperator">unary
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	802 operators</A> which can be used to resolve <A HREF="#Conflict">conflicts</A>. Operator precedence is also
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	803 referred to as <A HREF = "#Binding">binding</A>. Suppose that # and @ are two binary operators. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	804 question is how to interpret x # y @ z. If # has higher precedence than @, it is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	805 interpreted as (x#y)@z. On the other hand if # has lower precedence than @, it
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	806 would be x#(y@z). If # and @ have the same precedence then the question must be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	807 resolved by <A HREF="#Associativity">associativity</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	808 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	809 Note that all operators at the same precedence level must have the same
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	810 associativity.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	811 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	812 The situation is somewhat simpler for unary operators. If # and @ were both
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	813 prefix operators, or both suffix operators, there would be no ambiguity in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	814 interpretation, since neither # @ x and x # @ offer more than one possible
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	815 interpretation. The only difficulty arises when both a prefix and a suffix
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	816 operator are applied to the same operand.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	817 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	818 Suppose that # is a prefix operator and @ is a suffix operator. The question
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	819 then is how to interpret # x @. If # has higher precedence than @, it would be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	820 interpreted as (# x) @. On the other hand, if # has lower precedence than @, it
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	821 would be interpreted as # (x @). If # and @ have the same precedence then the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	822 question must be resolved by associativity.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	823 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	824 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	825 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	826
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	827 <DT><B><A NAME="Production">Production</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	828 <DD> Productions are the mechanism used to describe how complex input
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	829 structures are built up out of simpler ones. Each production has a left side and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	830 a right side. The right side, or <A HREF="#GrammarRule">grammar rule</A>,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	831 is a sequence of <A HREF="#RuleElement">rule elements</A>,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	832 which may represent either <A HREF="#Terminal">terminal tokens</A> or
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	833 <A HREF="#Nonterminal">nonterminal tokens</A>. The left side
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	834 is a list of <A HREF="#ReductionToken">reduction tokens</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	835 In most cases there would be only a single
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	836 reduction token. Productions with more than one <A HREF="#Token">token</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	837 on the left side are
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	838 called <A HREF = "#SemanticallyDetermined">semantically determined productions</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	839 <p>The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	840 "<CODE>-></CODE>" symbol is used
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	841 to separate the left side from the right side.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	842
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	843 If you have several
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	844 productions with the same left hand side, you can avoid
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	845 rewriting the left hand side either by using '\|' or by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	846 using another "->".
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	847 <p>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	848
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	849 A <A HREF="#NullProduction"> null production</A>, or empty right hand side, cannot
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	850 follow a '\|'.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	851 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	852 Productions may be written thus:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	853 <pre>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	854 name
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	855 -> letter
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	856 -> name, digit
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	857 </pre>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	858 This could also be written
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	859 <pre>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	860 name -> letter \| name, digit
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	861 </pre>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	862 In order to accommodate semantic analysis of the data,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	863 you may attach to any grammar rule a <A HREF="#ReductionProcedure">reduction
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	864 procedure</A> which will be executed when the rule is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	865 identified. Each token may have a <A HREF="#SemanticValue"> semantic value</A>. By
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	866 using <A HREF="#ParameterAssignment"> parameter assignments</A>, you may provide the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	867 reduction procedure with access to the semantic values of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	868 tokens that comprise the grammar rule. When it finishes, the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	869 reduction procedure may return a value which will be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	870 saved on the <A HREF="#ParserValueStack"> parser value stack</A> as the semantic value of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	871 <A HREF="#ReductionToken">reduction token</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	872
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	873 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	874 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	875
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	876 <DT><B><A NAME="ReduceAction">Reduce Action</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	877 <DD> The reduce action is one of the four <A HREF="#ParserAction">actions</A> of a traditional parsing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	878 engine. The reduce action is performed when the <A HREF="#Parser">parser</A> has succeeded in matching
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	879 all the elements of a <A HREF="#GrammarRule">grammar rule</A> and the next input <A HREF="#Token">token</A> is not erroneous.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	880 Reducing the grammar rule amounts to subtracting the length of the rule from the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	881 parser stack index, identifying the <A HREF="#ReductionToken">reduction token</A>, stacking its
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	882 <A HREF="#SemanticValue">semantic value</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	883 and then doing a <A HREF="#ShiftAction">shift action</A> with the reduction token as though it had been
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	884 input directly.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	885 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	886 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	887
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	888 <DT><B><A NAME="ReduceReduce">Reduce-Reduce Conflict</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	889 <DD> A <A HREF = "#Grammar">grammar</A> has a "reduce-reduce" conflict at some state if a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	890 single <A HREF="#Token">token</A> turns out to be a <A HREF="#ReducingToken">reducing token</A> for more than one <A HREF="#CompletedRule">completed rule</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	891 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	892 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	893
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	894 <DT><B><A NAME="ReducingToken">Reducing Token</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	895 <DD> In a state with more than one <A HREF="#CompletedRule">completed rule</A>, your <A HREF="#Parser">parser</A> must be able to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	896 determine which one was actually found. AnaGram deals with this problem by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	897 looking at all the states the parser will branch to once each rule is reduced.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	898 The acceptable input <A HREF="#Token">tokens</A> for those states are the "reducing tokens"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	899 for the completed rules in the state under investigation. If there is a single
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	900 token which is a reducing token for more than one rule, then the <A HREF = "#Grammar">grammar</A> is said
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	901 to have a <A HREF="#ReduceReduce">reduce-reduce conflict</A> at that state. If in a particular state there
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	902 is both a <A HREF="#ShiftAction">shift action</A> and a <A HREF="#ReduceAction">reduce action</A> for the same token the grammar is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	903 said to have a <A HREF="#ShiftReduce">shift-reduce conflict</A> in that state.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	904 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	905 A reducing token is not the same as a <A HREF="#ReductionToken">reduction token</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	906 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	907 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	908 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	909
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	910 <DT><B><A NAME="ReductionProcedure">Reduction Procedure</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	911 <DD> A "reduction procedure" is a function you write which your
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	912 <A HREF="#Parser">parser</A> executes when it has identified the <A HREF="#GrammarRule">grammar rule</A> to which the reduction
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	913 procedure is attached in your <A HREF = "#Grammar">grammar</A>. There are two formats for reduction
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	914 procedures, depending on the size and complexity of the procedure.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	915 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	916 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	917
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	918 <DT><B><A NAME="ReductionToken">Reduction Token</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	919 <DD> A <A HREF="#Token">token</A> which appears on the left side of a <A HREF="#Production">production</A> is called a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	920 reduction token. It is so called because when the <A HREF="#GrammarRule">grammar rule</A> on the right side
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	921 of the production is matched in the input stream, your <A HREF="#Parser">parser</A> will <A HREF="#ReduceAction">"reduce"</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	922 the sequence of tokens which matches the rule by replacing the sequence of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	923 tokens with the reduction token. Note that, if more than one reduction token is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	924 specified, your <A HREF="#ReductionProcedure">reduction procedure</A> should choose the exact one. If it does not,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	925 your parser will use the leftmost syntactically correct one in the list as the default.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	926 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	927 A reduction token is not the same as a <A HREF="#ReducingToken">reducing token</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	928 </P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	929 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	930 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	931
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	932 <DT><B><A NAME="Resynchronization">Resynchronization</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	933 <DD> "Resynchronization" is the process of getting your <A HREF="#Parser">parser</A> back
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	934 in step with its input after encountering a syntax error. As such, it is one
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	935 method of error recovery. Of course, you would resynchronize only if it
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	936 is necessary to continue after the error. There are several options available
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	937 when using AnaGram. You could use the auto resynch option, which causes AnaGram
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	938 to incorporate an automatic resynchronizing procedure into your parser, or you
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	939 could use the error resynch option, which is similar to the technique used by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	940 YACC programmers.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	941 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	942
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	943 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	944 <DT><B><A NAME="RuleElement">Rule Element</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	945 <DD> A <A HREF="#GrammarRule">grammar rule</A> is a list of "rule elements", separated by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	946 commas. Rule elements may be <A HREF="#Token">token</A> names, <A HREF="#CharacterSets">character sets</A>, keywords, immediate
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	947 actions, or <A HREF="#VirtualProduction">virtual productions</A>. When AnaGram encounters a rule element for
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	948 which no token presently exists, it creates one.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	949 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	950 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	951
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	952 <DT><B><A NAME="SemanticAction">Semantic Action</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	953 <DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	954 A semantic action is a piece of C or C++ code that is executed when
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	955 a <A HREF="#GrammarRule">grammar rule</A> has been identified by a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	956 <A HREF="#Parser">parser</A>. Semantic actions are also called
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	957 <A HREF="#ReductionProcedure">reduction procedures</A>, since they
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	958 are executed when a grammar rule is <A
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	959 HREF="#ReduceAction">reduced</A> to the token on the left side of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	960 <A HREF="#Production">production.</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	961 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	962 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	963
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	964 <DT><B><A NAME="SemanticValue">Semantic Value</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	965 <DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	966 <A HREF="#Token">Tokens</A>, whether <A HREF="#Terminal">terminal</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	967 or <A HREF="#Nonterminal">nonterminal</A>, may have a semantic value.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	968 In the case of terminal tokens, this may be a value assigned by the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	969 <A HREF="#LexicalScanner">lexical scanner</A> or, if the parser is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	970 using direct character input, it will be the ascii value of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	971 character itself. The values of nonterminal tokens are created by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	972 <A HREF="#ReductionProcedure">reduction procedures</A>. As a parse
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	973 progresses, token values are <A HREF="#ShiftAction">shifted</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	974 onto the stack, so that in a reduction procedure, the values of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	975 tokens that comprise the <A HREF="#GrammarRule">grammar rule</A> that
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	976 is being <A HREF="#ReduceAction">reduced</A> are available
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	977 for inspection.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	978 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	979 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	980
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	981 <DT><B><A NAME="SemanticallyDetermined">Semantically Determined Production</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	982 <DD> A "semantically determined production" is one which has more
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	983 than one <A HREF="#ReductionToken">reduction token</A> specified on the left side of the production. You would
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	984 write such a <A HREF="#Production">production</A> when the reduction tokens are syntactically
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	985 indistinguishable. The <A HREF="#ReductionProcedure">reduction procedure</A> may then specify which of the listed
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	986 reduction tokens the <A HREF="#GrammarRule">grammar rule</A> is to reduce to based on semantic
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	987 considerations. If there is no reduction procedure, or the reduction procedure
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	988 does not specify a reduction token, the <A HREF="#Parser">parser</A> will use the leftmost syntactically correct token.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	989
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	990 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	991 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	992
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	993 <DT><B><A NAME="SetExpression">Set Expression</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	994 <DD> A set expression is an algebraic expression used to define a <A HREF="#CharacterSets">character set</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	995 in terms of individual characters, ranges of characters, and/or other sets of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	996 characters as constructed using <A HREF="#SetComplement">complements</A>, <A HREF="#SetUnion">unions</A>, <A HREF="#SetIntersection">intersections</A>, and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	997 <A HREF="#SetDifference">differences</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	998 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	999 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1000
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1001 <DT><B><A NAME="ShiftAction">Shift Action</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1002 <DD> The shift action is one of the four <A HREF="#ParserAction">actions</A> of a traditional parsing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1003 engine. The shift action is performed when the input <A HREF="#Token">token</A> matches one of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1004 acceptable input tokens for the current parser state. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1005 <A HREF="#SemanticValue">semantic value</A> of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1006 token and the current state number are stacked, the parser stack index is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1007 incremented and the state number is set to a value determined by the previous
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1008 state and the input token.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1009 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1010 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1011
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1012 <DT><B><A NAME="ShiftReduce">Shift-Reduce Conflict</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1013 <DD> A "shift-reduce" conflict occurs if in some state there is a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1014 single <A HREF="#Token">token</A> that should be shifted, because it is legitimate input for one of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1015 the rules of the state, but should also be used to reduce some other rule
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1016 because it is a <A HREF="#ReducingToken">reducing token</A> for that rule.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1017 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1018 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1019 <DT><B><A NAME="SyntaxDirectedParsing">Syntax Directed Parsing</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1020 <DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1021 <P>Syntax directed parsing, or formal parsing, is an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1022 approach to building <A HREF="#Parser">parsers</A> based on formal language
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1023 theory. Given a suitable description of a language,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1024 called a <A HREF="#Grammar">grammar</A>, there are algorithms which can be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1025 used to create parsers for the language automatically.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1026 In this context, the set of all possible inputs to a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1027 program may be considered to constitute a language, and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1028 the rules for formulating the input to the program
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1029 constitute the grammar for the language.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1030
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1031 <P>The parsers built from a grammar have the advantage
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1032 that they can recognize any input that conforms to the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1033 rules, and can reject as erroneous any input that fails
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1034 to conform.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1035
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1036 <P>Since the program logic necessary to parse input is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1037 often extremely intricate, programs which use formal
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1038 parsing are usually much more reliable than those built
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1039 by hand. They are also much easier to maintain, since
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1040 it is much easier to modify a grammar specification
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1041 than it is to modify complex program logic.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1042
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1043 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1044 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1045
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1046 <DT><B><A NAME="Terminal">Terminal Token</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1047 <DD> A "terminal token" is a <A HREF="#Token">token</A> which does not appear on the left
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1048 side of a <A HREF="#Production">production</A>. It represents, therefore, a basic unit of input to your
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1049 <A HREF="#Parser">parser</A>. If the input to your parser consists of ascii characters, you may define
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1050 terminal tokens explicitly as ascii characters or as <A HREF="#CharacterSets">sets of ascii characters</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1051 If you have an input procedure which produces numeric codes, you may define the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1052 terminal tokens directly in terms of these numeric codes.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1053 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1054 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1055
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1056 <DT><B><A NAME="Token">Token</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1057 <DD> Tokens are the units with which your <A HREF="#Parser">parser</A> works. There are two kinds of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1058 tokens: <A HREF="#Terminal">terminal tokens</A> and <A HREF="#Nonterminal">nonterminal tokens</A>. These latter are identified by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1059 the parser as sequences of tokens. The grouping of tokens into more complex
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1060 tokens is governed by the <A HREF="#GrammarRule">grammar rules</A>, or <A HREF="#Production">productions</A> in your <A HREF = "#Grammar">grammar</A>. In your
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1061 grammar, tokens may be denoted by token names, by <A HREF="#VirtualProduction">virtual productions</A>, by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1062 immediate actions, by explicit character representations, or by expressions
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1063 which yield <A HREF="#CharacterSets">character sets</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1064 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1065 A "token" should be thought of more or less as being something like a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1066 cloakroom token. Imagine you had taken a kindergarten class to the museum and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1067 all the kids checked their coats. Each one gets a token. What is the probability
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1068 of losing one? You take all of the tokens from the children, put them in a paper
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1069 bag, tie it up, and check it. You get one token in return. We would say that the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1070 kids' coats represent the actual input to the system, their individual tokens
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1071 are the <A HREF="#Terminal">terminal tokens</A>, and your one token which enables you to redeem the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1072 paper bag is a <A HREF="#Nonterminal">nonterminal token</A>. Nonterminal tokens are just single token
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1073 numbers to represent the result of compacting a sequence of more primitive
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1074 tokens.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1075 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1076 Actually, the word "token" is commonly used to refer to a number of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1077 apparently different things. The tokens you use in a grammar are abstract. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1078 tokens identified by a parser are concrete instances of the abstract tokens in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1079 the grammar. Furthermore, we have to identify tokens in some manner, so we have
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1080 token names and token numbers with which to refer to particular tokens. As a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1081 result the word "token", in any particular context, may refer directly
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1082 to either an abstract token, or a concrete instance of an abstract token, or may
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1083 refer only indirectly to the token by means of a token name or token number.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1084 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1085 As an example, consider a C compiler which has a lexical scanner to identify
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1086 input tokens. According to Kernighan and Ritchie, there are six classes of C
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1087 tokens: identifiers, keywords, constants, string literals, operators, and other
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1088 separators. Consider a particular token, a hexadecimal constant, 0XF00. When the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1089 lexical scanner hands this over to the parser, it has to provide an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1090 identification code which says what kind of token it is, a hexadecimal constant,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1091 as well as the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1092 <A HREF="#SemanticValue">"semantic value"</A> of the token,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1093 3840. The identification code is usually an integer value,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1094 determined by the designer of the lexical scanner, which by agreement
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1095 with the designer of the parser uniquely represents a hexadecimal
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1096 constant. This identification code can be thought of as an external
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1097 token number.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1098
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1099 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1100 The grammar for the parser, on the other hand, has a token, "HEXconstant",
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1101 let us say, to represent the abstract usage of hexadecimal constants in the C
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1102 language. When AnaGram, or any other parser generator for that matter, analyzes
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1103 the grammar, it assigns its own reference number to identify "HEXconstant".
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1104 This reference number can be thought of as an internal token number to contrast
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1105 it with the external token number provided by the lexical scanner. The parsers
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1106 AnaGram builds contain a table, ag_ tcv, which provides a translation from the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1107 external to the internal token number. Both of these token numbers, of course,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1108 differ from the semantic value of the token, in this case, 3840.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1109 </P><P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1110 Even when an AnaGram parser is using simple character input, the word "token"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1111 may represent several different things. Suppose a grammar has a token 'A-Z',
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1112 which represents the set of upper case letters. There will be an internal token
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1113 number, assigned by AnaGram, which identifies the (abstract) token in parser
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1114 tables. The actual (concrete) input token to a parser will, however, be a single
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1115 letter, say "Q". In this case, the ascii value of the character "Q",
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1116 81, is used both as the external token number and as the semantic value of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1117 token.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1118 </P><P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1119 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1120
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1121 <DT><B><A NAME="UnaryOperator">Unary Operator</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1122 <DD>A "unary operator" is a <A HREF="#Token">token</A> which represents
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1123 some sort of operation which operates on a single entity to produce a new
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1124 resultant entity. It is normally represented by a symbol which is written either
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1125 preceding the operand or following the operand. In the first case it is called a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1126 "prefix operator" and in the second case a "suffix operator".
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1127 </P><P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1128 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1129
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1130 <DT><B><A NAME="SetUnion">Union</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1131 <DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1132 The union of two sets is the set of all elements that are to be found in one or
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1133 another of the two sets. In an AnaGram syntax file the union of two <A HREF="#CharacterSets">character
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1134 sets</A> A and B is represented using the plus sign, as in A + B. The union operator
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1135 has the same <A HREF="#Precedence">precedence</A> as the <A HREF="#SetDifference">difference</A> operator: lower than that of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1136 <A HREF="#SetIntersection">intersection</A> and <A HREF="#SetComplement">complement</A>. The union operator is <A HREF="#Associativity">left associative</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1137 <P></P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1138 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1139
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1140 <DT><B><A NAME="VirtualProduction">Virtual Production</A></B></DT>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1141 <DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1142 <P>Virtual productions are a special short hand
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1143 representation of <A HREF="#GrammarRule">grammar rules</A> which can be used to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1144 indicate a choice of inputs. They are an important
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1145 convenience, especially useful when you are first
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1146 building a <A HREF="#Grammar">grammar</A>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1147
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1148 <P>AnaGram rewrites virtual productions, so that when you
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1149 look at the syntax tables in AnaGram, there will be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1150 actual <A HREF="#Production">productions</A> replacing the virtual productions.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1151
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1152 <P>A virtual production appears as one of the <A HREF="#RuleElement">rule
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1153 elements</A> in a <A HREF="#GrammarRule">grammar rule</A>, i.e. as one of the members
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1154 of the list on the right side of a production.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1155
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1156 <P>The simplest virtual production is the "optional"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1157 <A HREF="#Token">token</A>. If x is an arbitrary token, x? can be used to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1158 indicate an optional x.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1159
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1160 <P>Related virtual productions are x... and x?... where
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1161 the three dots indicate repetition. x... represents an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1162 arbitrary number of occurrences of x, but at least one.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1163 x?... represents zero or more occurrences of x.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1164
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1165 <P>The remaining virtual productions use curly or square
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1166 brackets to enclose a sequence of rules. The brackets
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1167 may be followed variously by nothing, a string of three
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1168 dots, or a slash, to indicate the choices to be made
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1169 from the rules. Note that rules may be used, not merely
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1170 tokens.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1171
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1172 <P>If r1 through rn are a set of grammar rules, then
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1173 <PRE> {r1 \| r2 \| ... \| rn} </PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1174 is a virtual production that allows a choice of exactly
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1175 one of the rules. Similarly,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1176 <PRE> {r1 \| r2 \| ... \| rn}... </PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1177 is a virtual production that allows a choice of one or
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1178 more of the rules. And, finally,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1179 <PRE> {r1 \| r2 \| ... \| rn}/... </PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1180 is a virtual production that allows a choice of one or
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1181 more of the rules subject to the side condition that
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1182 rules must alternate, that is, that no rule can follow
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1183 itself immediately without the interposition of some
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1184 other rule. This is a case that is not particularly
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1185 easy to write by hand, but is quite useful in a number
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1186 of contexts.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1187
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1188 <P>If the above virtual productions are written with [ ]
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1189 instead of { }, they all become optional. [ ] is an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1190 optional choice, [ ]... is zero or more choices, and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1191 [ ]/... is zero or more alternating choices.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1192
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1193 <P><A HREF="#NullProduction">Null productions</A> are not permitted in virtual
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1194 productions in those cases where they would cause an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1195 intrinsic ambiguity.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1196
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1197 <P>You may use a definition statement to assign a name to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1198 a virtual production.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1199
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1200 </DD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1201
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1202 </DL>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1203
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1204
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1205 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1206 <BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1207
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1208 <IMG ALIGN="bottom" SRC="images/rbline6j.gif" ALT="----------------------"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1209 WIDTH=1010 HEIGHT=2 >
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1210 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1211 <IMG ALIGN="right" SRC="images/pslrb6d.gif" ALT="Parsifal Software"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1212 WIDTH=181 HEIGHT=25>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1213 <BR CLEAR="right">
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1214 Back to <A HREF="index.html">Index</A>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1215 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1216 <ADDRESS><FONT SIZE="-1">
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1217 AnaGram parser generator - documentation<BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1218 Glossary<BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1219 Copyright © 1993-1999, Parsifal Software. <BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1220 All Rights Reserved.<BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1221 </FONT></ADDRESS>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1222
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1223 </BODY>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1224 </HTML>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1225
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	1226

Mercurial > ~dholland > hg > ag > index.cgi

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