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

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> Fahrenheit-Celsius Converter</TITLE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	5 </HEAD>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	6
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
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	9
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	10 <BODY BGCOLOR="#ffffff" BACKGROUND="tilbl6h.gif"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	11 TEXT="#000000" LINK="#0033CC"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	12 VLINK="#CC0033" ALINK="#CC0099">
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	13
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	14 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	15 <IMG ALIGN="right" SRC="../images/agrsl6c.gif" ALT="AnaGram"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	16 WIDTH=124 HEIGHT=30 >
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	17 <BR CLEAR="all">
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 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	23
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	24 <H1> Fahrenheit-Celsius Converter</H1>
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 <H2>Introduction</H2>
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 Conversion of temperatures from Fahrenheit to Celsius is a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	31 traditional starting point for learning how to use a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	32 programming language. This directory contains a graded sequence
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	33 of Fahrenheit to Celsius conversion programs, starting with
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	34 a very simple case and working up to one of some complexity.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	35 This sequence of programs illustrates an important aspect of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	36 syntax directed programming: In contrast to conventional
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	37 programming methods it is quite easy to begin with a simple
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	38 case and then extend it to more complex situations.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	39 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	40 All of these programs accept input from <tt>stdin</tt> and write
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	41 output to <tt>stdout</tt>. These programs are somewhat exceptional,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	42 since, except for FC5, they do not have any embedded C and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	43 therefore do not require explicit definition of a main
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	44 program.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	45 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	46 <tt>fc1</tt> is the first and simplest of the Fahrenheit to Celsius
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	47 conversion programs. It expects the user to type a positive
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	48 integer value, assumed to be a Fahrenheit temperature, which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	49 it converts to Celsius. It then exits.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	50 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	51 <tt>fc2</tt>, the next example, is a somewhat more interesting
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	52 Fahrenheit-Celsius converter. This time the input stream may
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	53 contain any number of temperatures, either Fahrenheit or
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	54 Celsius, each terminated by a newline character. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	55 program will continue until it encounters an end of file. If it
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	56 encounters a syntax error in the input, it will skip to the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	57 next newline character and continue. <tt>fc2</tt> has been set up to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	58 illustrate the usage of the File Trace feature of AnaGram.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	59 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	60 <tt>fc3</tt> adds two new features to <tt>fc2</tt>: It uses
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	61 floating point
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	62 arithmetic, so that it can deal with non-integral values,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	63 and it allows optional white space in the input, except
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	64 within numbers. In addition, it changes the output format,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	65 so that results are printed in degrees Kelvin, as well as in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	66 Fahrenheit and Celsius.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	67 <font size=-1>(Yes, we know that in Newspeak the official
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	68 usage is "Kelvins", not "degrees Kelvin". Shush.)</font>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	69 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	70 <tt>fc4</tt> illustrates a shift-reduce conflict which arose when
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	71 modifying the <tt>fc3</tt> grammar to allow input in degrees Kelvin.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	72 You should probably skip this example until you encounter a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	73 shift-reduce conflict in one of your own grammars. <tt>fc4a</tt> and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	74 <tt>fc4b</tt> are two different resolutions of the conflict.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	75 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	76 <tt>fc5</tt> illustrates the use of an event driven parser. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	77 actual grammar is the same as <tt>fc4b</tt>. The only difference is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	78 in the method of providing input to the parser.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	79 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	80
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	81 <H2>FC1</H2>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	82 <tt>fc1</tt> is the first and simplest of the Fahrenheit to Celsius
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	83 conversion programs. It expects the user to type an integer
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	84 value, assumed to be a Fahrenheit temperature, which it
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	85 converts to Celsius. It then exits.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	86 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	87 The following features of AnaGram are introduced in <tt>fc1</tt>:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	88 <UL>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	89 <LI> recursive definition of tokens </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	90 <LI> definition of a set as a range of characters</LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	91 <LI> token type declaration </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	92 <LI> default token type </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	93 <LI> passing token values to reduction procedures </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	94 <LI> long and short form reduction procedures </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	95 </UL>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	96
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	97 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	98 <tt>fc1</tt> defines two nonterminal tokens, "grammar", which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	99 describes the entire input stream, and "integer", which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	100 describes a simple unsigned integer value. "grammar", defined
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	101 by one production, describes the input as consisting of an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	102 "integer" followed by a newline character. There is a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	103 following reduction procedure to print out both the input
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	104 and converted values.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	105 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	106 "integer" is recursively defined by two productions. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	107 first production says that an "integer" may be represented
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	108 by a single decimal digit. '0-9' represents the set of ascii
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	109 characters on the range '0' through '9'. The token can be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	110 matched by any character from this set. The second
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	111 production contains the recursion. It says that the combination of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	112 any "integer" followed by another decimal digit is also an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	113 integer. Note that the left side is the same for these two
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	114 productions and it need not be repeated.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	115 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	116 Note the type cast preceding "integer". This type cast
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	117 defines the data type of the semantic value of "integer" to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	118 be int. When the parser stores a token value for "integer"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	119 on its value stack or retrieves a value from the stack, the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	120 type of the data transmitted will be int.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	121 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	122 Since there is no type cast for the token "grammar", the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	123 data type for the semantic value of "grammar" is given by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	124 the "default token type" configuration parameter, which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	125 defaults to void.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	126 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	127 The semantic values of the tokens in a grammar rule may be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	128 passed to the associated reduction procedure. The name of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	129 the variable in the reduction procedure is simply appended
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	130 to the token name or expression in the rule with a colon as
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	131 a separator.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	132 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	133 All three reduction procedures in <tt>fc1</tt> operate on
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	134 the semantic
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	135 values of tokens on the parser stack as parameters. In
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	136 the first reduction procedure, the variable <tt>f</tt> represents the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	137 value of the integer typed by the user. It is taken as a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	138 Fahrenheit temperature and converted to Celsius by the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	139 reduction procedure. This reduction procedure uses the long
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	140 form, consisting of an equal sign followed by a block of C
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	141 code.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	142 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	143 The reduction procedures for the two productions for "integer"
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	144 convert the integer from ascii form as typed by the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	145 user to binary form. The first reduction procedure
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	146 calculates the value of a single digit integer. The second
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	147 reduction procedure calculates the value for an integer with more
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	148 than one digit. Notice that these reduction procedures both
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	149 use the short form: a C expression terminated by a semicolon.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	150 The value of the expression is saved as the semantic
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	151 value of the reduced token.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	152 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	153
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	154 <H3>Testing FC1</H3>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	155 Run AnaGram and build a parser, <tt>fc1.c</tt>. Compile it
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	156 and link it
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	157 with your C compiler. Run <tt>fc1</tt> from the command line.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	158 Type an integer and press
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	159 Enter. <tt>fc1</tt> will print out Fahrenheit and Celsius
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	160 temperatures.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	161 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	162
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	163
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	164 <H2>FC2</H2>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	165 The next example of a syntax file, <tt>fc2.syn</tt>, is a somewhat
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	166 more interesting Fahrenheit-Celsius converter. This time the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	167 input stream may contain any number of temperatures. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	168 program will continue until it encounters an end of file. If
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	169 it encounters a syntax error in the input, it will skip to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	170 the next newline character and continue. <tt>fc2</tt> has
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	171 been set up
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	172 to illustrate the File Trace feature of AnaGram.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	173 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	174 The following features of AnaGram are introduced in <tt>fc2</tt>:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	175 <UL>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	176 <LI> configuration section </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	177 <LI> character set defined by set union </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	178 <LI> end of file token </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	179 <LI> virtual productions </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	180 <LI> use of '?' to define a virtual production </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	181 <LI> error token resynchronization </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	182 <LI> File Trace </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	183 </UL>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	184 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	185 <tt>fc2</tt> allows the temperature values to be signed
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	186 integers which
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	187 may be either Fahrenheit or Celsius, as determined by a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	188 following 'f' or 'c'. Each temperature value to be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	189 converted must be followed by a newline. Spaces in the input
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	190 are not allowed.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	191 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	192 To facilitate testing, a configuration section has been
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	193 added at the beginning of the file to set two configuration
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	194 parameters, discussed below. The lines specifying the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	195 parameters have been labeled C1 and C2 at the right margin
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	196 to make them easy to refer to in this documentation.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	197 Similarly, productions have been labeled P1, P2, etc.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	198 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	199 After the configuration section, an end of file token, eof,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	200 is defined. Remember that when using stream I/O, the end of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	201 file is signalled by a -1.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	202 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	203 The first production, P1, describes the entire input file as
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	204 an optional sequence of temperatures followed by an end of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	205 file.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	206 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	207 The expression <CODE>[temperature, '\n']...</CODE> is a "virtual
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	208 production". The square brackets indicate the rule inside the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	209 brackets is optional. The ellipsis (<CODE>...</CODE>)
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	210 indicates that the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	211 rule may be repeated an arbitrary number of times.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	212 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	213 Productions P2 and P3 define "temperature" in the normal
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	214 case. Production P4 controls error recovery, described
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	215 below.In AnaGram, <CODE>'f' + 'F'</CODE> represents the set
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	216 of characters
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	217 containing both upper and lower case 'f'. (The plus sign is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	218 the union operator of set theory.) Either an upper or lower
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	219 case 'f' in the input will match this set. <CODE>'c' +
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	220 'C'</CODE> is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	221 similarly interpreted. Thus a temperature consists of a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	222 number followed by an 'f' or 'c' which can be either upper
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	223 or lower case. The reduction procedures, of course, are
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	224 different for 'f' and 'c'.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	225 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	226 Productions P5 and P6 define "number" as consisting of an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	227 integer with an optional sign. <CODE>'+'?</CODE> is a virtual production.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	228 The question mark indicates that the preceding element, in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	229 this case the plus sign, is optional. These productions
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	230 allow you to write numbers in the form 17, +17, or -17.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	231 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	232 Productions P7 and P8 define "integer" exactly as in <tt>fc1</tt>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	233 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	234
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	235 <H3> Recovering and Continuing after a Syntax Error </H3>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	236 The production P4 controls error recovery. "error" is a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	237 special token in an AnaGram grammar, which can be matched by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	238 any sequence of input which contains a syntax error. If your
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	239 grammar has an error token, when your parser encounters a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	240 syntax error it looks to see if there is an error token to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	241 match with the syntax error. If "error" is not admissible in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	242 the current state, it discards the previous token on the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	243 input stack and looks again. It continues until it gets back
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	244 to a state where "error" is acceptable input or the stack is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	245 empty. If the stack is empty, it terminates the parse.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	246 Otherwise, it then looks to see if the next input token is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	247 admissible. If so, the parse continues. If not, the token is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	248 discarded and the parser reads input until it finds an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	249 acceptable token or the end of file. In this example, the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	250 parser will read characters until it finds a newline character
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	251 At this point the parse will continue as though nothing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	252 had happened. This process is called "error token
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	253 resynchronization". It is one of several ways to continue after a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	254 parser detects a syntax error in its input stream.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	255 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	256
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	257
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	258 <H3> Configuration Parameters </H3>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	259 Two configuration parameters have been set in the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	260 configuration section of <tt>fc2</tt> to facilitate testing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	261 using the File
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	262 Trace. The first, test file mask, limits the choice of test
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	263 files to be used with the File Trace option to files with
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	264 the extension <tt>.fc2</tt>. The second, traditional engine, turns
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	265 off certain optimizations AnaGram normally builds into its
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	266 parsers. When the traditional engine switch is set, the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	267 parsers AnaGram builds use only the four traditional parser
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	268 actions: shift, reduce, error, and accept. Otherwise,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	269 AnaGram parsers use a number of compound actions in order to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	270 reduce the size of the parsing tables and increase the speed
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	271 of the parser. In this case, the traditional engine switch
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	272 has been turned on in order to make the behavior of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	273 parser as seen with the File Trace correspond to textbook
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	274 behavior.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	275 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	276
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	277 <H3> Testing FC2 </H3>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	278 Test <tt>fc2</tt> just as you did <tt>fc1</tt>: Run AnaGram
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	279 and build a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	280 parser, <tt>fc2.c</tt>. Compile it and link it with your C
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	281 compiler. Run
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	282 <tt>fc2</tt> from the command line. Type an integer, with or
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	283 without a sign, the letter 'f'
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	284 or 'c', and press Enter. <tt>fc2</tt> will print out Fahrenheit and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	285 Celsius temperatures. Repeat until you are satisfied the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	286 program works. Try making a few deliberate typos to test the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	287 error token resynchronization. Note that the parser
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	288 automatically provides error diagnostics. These diagnostics
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	289 are created by the default <tt>SYNTAX_ERROR</tt> macro.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	290 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	291 Type ^Z and Enter (Windows) or ^D (Unix) to generate an end
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	292 of file and end the program. (Of course, you
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	293 could also use ^C or ^Brk.)
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	294 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	295 Alternatively, you may use the test file, <tt>test.fc2</tt>,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	296 which has
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	297 been provided for use with the File Trace (see below).
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	298 Simply run <tt>fc2</tt> with input redirection to take input from
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	299 <tt>test.fc2</tt>. At the command prompt, type:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	300 <PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	301 fc2 < test.fc2
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	302 </PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	303 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	304
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	305 <H2> File Trace </H2>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	306 The File Trace feature of AnaGram allows you to test a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	307 grammar without actually building a parser. This enables you to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	308 completely decouple the debugging of the grammar from the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	309 debugging of the reduction procedures. You can try out test
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	310 files before you have written anything more than the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	311 grammar. This allows for very early testing in your projects.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	312 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	313
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	314 File Trace allows you to see in fine detail just exactly how
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	315 your parser will analyze an input file. A File Trace consists of a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	316 window with various panes so you can see what is going on,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	317 and an interpretive parser which works in the background.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	318 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	319 You can select File Trace from the Action
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	320 menu once you have analyzed your grammar. For the <tt>fc2</tt>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	321 example, you will be offered a choice of test files with
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	322 extension <tt>.fc2</tt>. A good choice would be <tt>test1.fc2</tt>.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	323 The File Trace window will show a Parser Stack
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	324 pane to your left, a Test File pane, which shows you the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	325 input file you are parsing, to your right, and a Rule Stack
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	326 pane across the bottom of the window.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	327 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	328 The way the File Trace parser works is this: Initially none of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	329 the test file has been parsed. If you double-click with the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	330 left mouse button at a point in the Test File pane, the parser
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	331 parses to that point. The unparsed part of the file will be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	332 colored differently from the parsed part (in the default
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	333 color scheme, parsed characters
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	334 have a lighter background). To back up the parse to a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	335 previous location, double-click at that spot, or single-click
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	336 and press Enter or the Synch Parse button at the bottom of
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	337 the File Trace window. To check a file for syntax errors, all
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	338 you need to do is to click the Parse File button. If there is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	339 a syntax error, the parse will not advance beyond the error
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	340 point. Normally, however, you will probably want to proceed
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	341 more deliberately, moving the cursor one character at a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	342 time.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	343 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	344 If you wish to see even finer detail, you may make the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	345 parser work in single step mode. by clicking on Single Step
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	346 or pressing Enter. Each time you click on the Single Step
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	347 button or press Enter, the parser will perform one parser
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	348 action. Note that in its normal configuration, AnaGram
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	349 produces parsers that use a number of parser actions more
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	350 complex than the traditional shift and reduce actions.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	351 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	352 The Parser Stack pane shows the levels of the parser stack, the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	353 state numbers on the stack and the tokens that have been
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	354 recognized so far.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	355 As you advance through the test file, you can see by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	356 looking at the Parser Stack pane how the parser stack changes
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	357 as characters are shifted in and reductions occur. The Rule
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	358 Stack pane is an alternate view of the parser stack showing
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	359 the grammar rules in play at any moment. Notice how the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	360 syntax file window is synched with the Rule Stack.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	361 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	362 If the parse position is not located at the blinking cursor,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	363 the Single Step button will be changed to read "Synch Parse".
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	364 Clicking on the button will move the parse position to the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	365 cursor.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	366 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	367 If you now click on tokens at various levels in the Token
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	368 Stack, the Test File characters corresponding to these tokens
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	369 will be highlighted. You can restart the parse at any level
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	370 by double-clicking just preceding the highlight. The Rule
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	371 Stack is also synched with the Token Stack and Test File
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	372 panes.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	373 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	374 You may interrupt the File Trace at any time to inspect any
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	375 other window without interfering with the File Trace.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	376 Whenever you come back to it, you can proceed as though
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	377 nothing has happened.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	378 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	379 If you have a long file, a complex grammar, or a (very) slow
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	380 computer, it can sometimes take a while for the parse to catch
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	381 up with the cursor. If you have a long test file and press
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	382 Parse File to move the cursor to the end of the file, the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	383 parser has a lot of computation to do to catch up.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	384 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	385 For further details about the File Trace, please refer to the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	386 AnaGram User's Guide and the on-line documentation.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	387 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	388 <BR>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	389
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	390
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	391 <H2> FC3 </H2>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	392 <tt>fc3</tt> adds two new features to <tt>fc2</tt>: It uses
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	393 floating point
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	394 arithmetic, so that it can deal with non-integral values,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	395 and it allows optional white space, including comments, in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	396 the input. In addition, it changes the output format, so
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	397 that results are printed in degrees Kelvin, as well as in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	398 Fahrenheit and Celsius.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	399 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	400 The following features of AnaGram are introduced in <tt>fc3</tt>:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	401 <UL>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	402 <LI> Setting the default token type </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	403 <LI> The "disregard" statement </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	404 <LI> The "lexeme" statement </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	405 <LI> Right recursion </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	406 <LI> Default value of a reduction token </LI>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	407 </UL>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	408 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	409
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	410 <H3> Floating Point Arithmetic </H3>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	411 To deal with floating point arithmetic, a number of new
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	412 productions have been added and two productions have been
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	413 changed. Productions P5 and P6 have been changed to define a
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	414 "number" in terms of an "unsigned number" instead of an
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	415 "integer". Productions P6a, P6b, and P6c define "unsigned
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	416 number" in terms of its integer part and its fraction part.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	417 Productions P9 and P10 define the fraction part of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	418 number. Note that "fraction" is described using right
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	419 recursion rather than left recursion. This makes the reduction
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	420 procedures neater. Since reduction does not occur until
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	421 a rule is complete, note that with right recursion each new
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	422 digit causes the stack depth to increase by one. You can
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	423 observe this with the File Trace.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	424 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	425 In order to replace integer arithmetic with floating point
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	426 arithmetic, statement C3 was added to the configuration
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	427 section of the grammar. It declares the default token type,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	428 the type assigned to nonterminal tokens absent a specific
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	429 declaration, to be "double". Since we are not interested in
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	430 values for "grammar" and "temperature", they have been
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	431 explicitly cast to "void".
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	432 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	433 Note that production P6a does not have a reduction procedure.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	434 If a rule has no reduction procedure the value of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	435 reduction token defaults to the value of the first element
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	436 in the rule. In this case, the value of "unsigned number",
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	437 in the absence of a reduction procedure, is taken to be the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	438 value of "integer".
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	439 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	440
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	441 <H3> Skipping White Space </H3>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	442 Two statements, C4 and C5, are used to skip over uninteresting
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	443 white space in the input to <tt>fc3</tt>. The "disregard" statement
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	444 instructs AnaGram to rewrite your grammar in a standard
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	445 way so that your parser will skip over any instance of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	446 "white space" token that occurs between lexemes, or lexical
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	447 units, in the input to your parser. Of course, you can use
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	448 any token name you wish in a "disregard" statement. You can
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	449 even have multiple "disregard" statements and all of the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	450 tokens you specify will be disregarded.
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 "lexeme" statement is used to declare that certain
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	453 nonterminal tokens are each to be considered as indivisible
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	454 lexical units, or lexemes, from the point of view of lexical
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	455 analysis, so that the "disregard" statement is inoperative
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	456 inside the nonterminal tokens listed. In this case, statement
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	457 C5 simply guarantees that white space will not be
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	458 allowed inside a number. All terminal tokens are automatically
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	459 lexemes. <!-- when not part of a larger lexeme. -->
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	460 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	461 <!--
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	462 It would be nice to rewrite this so the example expansion is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	463 vaguely close to syntactically legal.
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 To make your parser skip white space, AnaGram renames and
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	466 redefines the lexemes in your grammar and defines a number
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	467 of new tokens. For example, if '+' is a lexeme in your
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	468 grammar and your grammar is to disregard "white space",
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	469 AnaGram will rename the plus sign token as '+'%. It then
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	470 introduces a new production in your grammar as follows:
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	471 <PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	472 '+'
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	473 -> '+'%, white space?...
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	474 </PRE>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	475
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	476 This means that a plus sign followed by some white space
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	477 will now be treated the same, syntactically, as a plus sign
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	478 alone. The percent sign (a degree sign in AnaGram 1.x) is
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	479 used to indicate the original, or "pure",
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	480 definition of the token.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	481 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	482 Productions P11 and P12 together define what is meant by
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	483 white space in this grammar. P11 defines white space to
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	484 include blanks and tab characters. P12 includes C style
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	485 comments (not nested).
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	486 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	487 The white space defined in P11 and P12 does not include
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	488 newline characters. There is a good reason for this. The
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	489 grammar uses newline characters as delimiters, marking the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	490 end of a "temperature". In order to allow blank lines,
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	491 production P1 was modified to make the temperature optional.
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	492 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	493 To allow "//" style comments, a new token, "end of line",
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	494 defined by production P13, was added. In production P1, '\n'
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	495 was then replaced by "end of line".
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	496 <P>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	497
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	498 <H3> Testing FC3 </H3>
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	499 The "test file mask" was changed to use files with the
13d2b8934445 Import AnaGram (near-)release tree into Mercurial. David A. Holland parents: diff changeset	500 extension ".fc3" in the File Trace. TEST.FC3 can be used as

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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">

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3 <HEAD>

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4 <TITLE> Fahrenheit-Celsius Converter</TITLE>

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5 </HEAD>

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10 <BODY BGCOLOR="#ffffff" BACKGROUND="tilbl6h.gif"

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11 TEXT="#000000" LINK="#0033CC"

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12 VLINK="#CC0033" ALINK="#CC0099">

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13

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14 <P>

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15 <IMG ALIGN="right" SRC="../images/agrsl6c.gif" ALT="AnaGram"

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16 WIDTH=124 HEIGHT=30 >

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17 <BR CLEAR="all">

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18 Back to <A HREF="../index.html">Index</A>

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19 <P>

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20 <IMG ALIGN="bottom" SRC="../images/rbline6j.gif" ALT="----------------------"

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21 WIDTH=1010 HEIGHT=2 >

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22 <P>

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23

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24 <H1> Fahrenheit-Celsius Converter</H1>

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25 <IMG ALIGN="bottom" SRC="../images/rbline6j.gif" ALT="----------------------"

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26 WIDTH=1010 HEIGHT=2 >

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27 <P>

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28 <H2>Introduction</H2>

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29 <P>

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30 Conversion of temperatures from Fahrenheit to Celsius is a

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31 traditional starting point for learning how to use a

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32 programming language. This directory contains a graded sequence

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33 of Fahrenheit to Celsius conversion programs, starting with

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34 a very simple case and working up to one of some complexity.

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35 This sequence of programs illustrates an important aspect of

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36 syntax directed programming: In contrast to conventional

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37 programming methods it is quite easy to begin with a simple

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38 case and then extend it to more complex situations.

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39 <P>

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40 All of these programs accept input from <tt>stdin</tt> and write

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41 output to <tt>stdout</tt>. These programs are somewhat exceptional,

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42 since, except for FC5, they do not have any embedded C and

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43 therefore do not require explicit definition of a main

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44 program.

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45 <P>

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46 <tt>fc1</tt> is the first and simplest of the Fahrenheit to Celsius

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47 conversion programs. It expects the user to type a positive

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48 integer value, assumed to be a Fahrenheit temperature, which

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49 it converts to Celsius. It then exits.

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50 <P>

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51 <tt>fc2</tt>, the next example, is a somewhat more interesting

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52 Fahrenheit-Celsius converter. This time the input stream may

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53 contain any number of temperatures, either Fahrenheit or

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54 Celsius, each terminated by a newline character. The

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55 program will continue until it encounters an end of file. If it

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56 encounters a syntax error in the input, it will skip to the

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57 next newline character and continue. <tt>fc2</tt> has been set up to

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58 illustrate the usage of the File Trace feature of AnaGram.

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59 <P>

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60 <tt>fc3</tt> adds two new features to <tt>fc2</tt>: It uses

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61 floating point

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62 arithmetic, so that it can deal with non-integral values,

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63 and it allows optional white space in the input, except

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64 within numbers. In addition, it changes the output format,

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65 so that results are printed in degrees Kelvin, as well as in

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66 Fahrenheit and Celsius.

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67 <font size=-1>(Yes, we know that in Newspeak the official

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68 usage is "Kelvins", not "degrees Kelvin". Shush.)</font>

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69 <P>

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70 <tt>fc4</tt> illustrates a shift-reduce conflict which arose when

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71 modifying the <tt>fc3</tt> grammar to allow input in degrees Kelvin.

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72 You should probably skip this example until you encounter a

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73 shift-reduce conflict in one of your own grammars. <tt>fc4a</tt> and

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74 <tt>fc4b</tt> are two different resolutions of the conflict.

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75 <P>

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76 <tt>fc5</tt> illustrates the use of an event driven parser. The

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77 actual grammar is the same as <tt>fc4b</tt>. The only difference is

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78 in the method of providing input to the parser.

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79 <P>

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80

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81 <H2>FC1</H2>

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82 <tt>fc1</tt> is the first and simplest of the Fahrenheit to Celsius

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83 conversion programs. It expects the user to type an integer

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84 value, assumed to be a Fahrenheit temperature, which it

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85 converts to Celsius. It then exits.

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86 <P>

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87 The following features of AnaGram are introduced in <tt>fc1</tt>:

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88 <UL>

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89 <LI> recursive definition of tokens </LI>

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90 <LI> definition of a set as a range of characters</LI>

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91 <LI> token type declaration </LI>

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92 <LI> default token type </LI>

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93 <LI> passing token values to reduction procedures </LI>

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94 <LI> long and short form reduction procedures </LI>

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95 </UL>

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96

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97 <P>

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98 <tt>fc1</tt> defines two nonterminal tokens, "grammar", which

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99 describes the entire input stream, and "integer", which

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100 describes a simple unsigned integer value. "grammar", defined

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101 by one production, describes the input as consisting of an

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102 "integer" followed by a newline character. There is a

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103 following reduction procedure to print out both the input

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104 and converted values.

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105 <P>

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106 "integer" is recursively defined by two productions. The

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107 first production says that an "integer" may be represented

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108 by a single decimal digit. '0-9' represents the set of ascii

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109 characters on the range '0' through '9'. The token can be

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110 matched by any character from this set. The second

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111 production contains the recursion. It says that the combination of

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112 any "integer" followed by another decimal digit is also an

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113 integer. Note that the left side is the same for these two

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114 productions and it need not be repeated.

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115 <P>

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116 Note the type cast preceding "integer". This type cast

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117 defines the data type of the semantic value of "integer" to

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118 be int. When the parser stores a token value for "integer"

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119 on its value stack or retrieves a value from the stack, the

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120 type of the data transmitted will be int.

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121 <P>

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122 Since there is no type cast for the token "grammar", the

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123 data type for the semantic value of "grammar" is given by

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124 the "default token type" configuration parameter, which

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125 defaults to void.

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126 <P>

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127 The semantic values of the tokens in a grammar rule may be

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128 passed to the associated reduction procedure. The name of

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129 the variable in the reduction procedure is simply appended

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130 to the token name or expression in the rule with a colon as

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131 a separator.

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132 <P>

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133 All three reduction procedures in <tt>fc1</tt> operate on

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134 the semantic

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135 values of tokens on the parser stack as parameters. In

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136 the first reduction procedure, the variable <tt>f</tt> represents the

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137 value of the integer typed by the user. It is taken as a

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138 Fahrenheit temperature and converted to Celsius by the

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139 reduction procedure. This reduction procedure uses the long

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140 form, consisting of an equal sign followed by a block of C

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141 code.

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142 <P>

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143 The reduction procedures for the two productions for "integer"

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144 convert the integer from ascii form as typed by the

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145 user to binary form. The first reduction procedure

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146 calculates the value of a single digit integer. The second

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147 reduction procedure calculates the value for an integer with more

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148 than one digit. Notice that these reduction procedures both

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149 use the short form: a C expression terminated by a semicolon.

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150 The value of the expression is saved as the semantic

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151 value of the reduced token.

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152 <P>

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153

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154 <H3>Testing FC1</H3>

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155 Run AnaGram and build a parser, <tt>fc1.c</tt>. Compile it

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156 and link it

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157 with your C compiler. Run <tt>fc1</tt> from the command line.

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158 Type an integer and press

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159 Enter. <tt>fc1</tt> will print out Fahrenheit and Celsius

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160 temperatures.

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161 <P>

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162

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163

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164 <H2>FC2</H2>

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165 The next example of a syntax file, <tt>fc2.syn</tt>, is a somewhat

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166 more interesting Fahrenheit-Celsius converter. This time the

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167 input stream may contain any number of temperatures. The

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168 program will continue until it encounters an end of file. If

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169 it encounters a syntax error in the input, it will skip to

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170 the next newline character and continue. <tt>fc2</tt> has

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171 been set up

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172 to illustrate the File Trace feature of AnaGram.

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173 <P>

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174 The following features of AnaGram are introduced in <tt>fc2</tt>:

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175 <UL>

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176 <LI> configuration section </LI>

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177 <LI> character set defined by set union </LI>

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178 <LI> end of file token </LI>

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179 <LI> virtual productions </LI>

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180 <LI> use of '?' to define a virtual production </LI>

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181 <LI> error token resynchronization </LI>

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182 <LI> File Trace </LI>

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183 </UL>

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184 <P>

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185 <tt>fc2</tt> allows the temperature values to be signed

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186 integers which

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187 may be either Fahrenheit or Celsius, as determined by a

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188 following 'f' or 'c'. Each temperature value to be

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189 converted must be followed by a newline. Spaces in the input

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190 are not allowed.

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191 <P>

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192 To facilitate testing, a configuration section has been

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193 added at the beginning of the file to set two configuration

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194 parameters, discussed below. The lines specifying the

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195 parameters have been labeled C1 and C2 at the right margin

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196 to make them easy to refer to in this documentation.

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197 Similarly, productions have been labeled P1, P2, etc.

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198 <P>

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199 After the configuration section, an end of file token, eof,

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200 is defined. Remember that when using stream I/O, the end of

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201 file is signalled by a -1.

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202 <P>

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203 The first production, P1, describes the entire input file as

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204 an optional sequence of temperatures followed by an end of

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205 file.

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206 <P>

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207 The expression <CODE>[temperature, '\n']...</CODE> is a "virtual

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208 production". The square brackets indicate the rule inside the

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209 brackets is optional. The ellipsis (<CODE>...</CODE>)

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210 indicates that the

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211 rule may be repeated an arbitrary number of times.

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212 <P>

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213 Productions P2 and P3 define "temperature" in the normal

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214 case. Production P4 controls error recovery, described

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215 below.In AnaGram, <CODE>'f' + 'F'</CODE> represents the set

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216 of characters

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217 containing both upper and lower case 'f'. (The plus sign is

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218 the union operator of set theory.) Either an upper or lower

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219 case 'f' in the input will match this set. <CODE>'c' +

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220 'C'</CODE> is

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221 similarly interpreted. Thus a temperature consists of a

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222 number followed by an 'f' or 'c' which can be either upper

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223 or lower case. The reduction procedures, of course, are

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224 different for 'f' and 'c'.

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225 <P>

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226 Productions P5 and P6 define "number" as consisting of an

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227 integer with an optional sign. <CODE>'+'?</CODE> is a virtual production.

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228 The question mark indicates that the preceding element, in

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229 this case the plus sign, is optional. These productions

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230 allow you to write numbers in the form 17, +17, or -17.

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231 <P>

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232 Productions P7 and P8 define "integer" exactly as in <tt>fc1</tt>.

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233 <P>

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234

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235 <H3> Recovering and Continuing after a Syntax Error </H3>

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236 The production P4 controls error recovery. "error" is a

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237 special token in an AnaGram grammar, which can be matched by

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238 any sequence of input which contains a syntax error. If your

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239 grammar has an error token, when your parser encounters a

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240 syntax error it looks to see if there is an error token to

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241 match with the syntax error. If "error" is not admissible in

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242 the current state, it discards the previous token on the

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243 input stack and looks again. It continues until it gets back

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244 to a state where "error" is acceptable input or the stack is

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245 empty. If the stack is empty, it terminates the parse.

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246 Otherwise, it then looks to see if the next input token is

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247 admissible. If so, the parse continues. If not, the token is

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248 discarded and the parser reads input until it finds an

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249 acceptable token or the end of file. In this example, the

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250 parser will read characters until it finds a newline character

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251 At this point the parse will continue as though nothing

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252 had happened. This process is called "error token

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253 resynchronization". It is one of several ways to continue after a

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254 parser detects a syntax error in its input stream.

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255 <P>

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256

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257

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258 <H3> Configuration Parameters </H3>

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259 Two configuration parameters have been set in the

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260 configuration section of <tt>fc2</tt> to facilitate testing

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261 using the File

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262 Trace. The first, test file mask, limits the choice of test

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263 files to be used with the File Trace option to files with

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264 the extension <tt>.fc2</tt>. The second, traditional engine, turns

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265 off certain optimizations AnaGram normally builds into its

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266 parsers. When the traditional engine switch is set, the

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267 parsers AnaGram builds use only the four traditional parser

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268 actions: shift, reduce, error, and accept. Otherwise,

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269 AnaGram parsers use a number of compound actions in order to

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270 reduce the size of the parsing tables and increase the speed

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271 of the parser. In this case, the traditional engine switch

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272 has been turned on in order to make the behavior of the

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273 parser as seen with the File Trace correspond to textbook

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274 behavior.

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275 <P>

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276

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277 <H3> Testing FC2 </H3>

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278 Test <tt>fc2</tt> just as you did <tt>fc1</tt>: Run AnaGram

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279 and build a

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280 parser, <tt>fc2.c</tt>. Compile it and link it with your C

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281 compiler. Run

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282 <tt>fc2</tt> from the command line. Type an integer, with or

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283 without a sign, the letter 'f'

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284 or 'c', and press Enter. <tt>fc2</tt> will print out Fahrenheit and

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285 Celsius temperatures. Repeat until you are satisfied the

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286 program works. Try making a few deliberate typos to test the

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287 error token resynchronization. Note that the parser

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288 automatically provides error diagnostics. These diagnostics

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289 are created by the default <tt>SYNTAX_ERROR</tt> macro.

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290 <P>

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291 Type ^Z and Enter (Windows) or ^D (Unix) to generate an end

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292 of file and end the program. (Of course, you

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293 could also use ^C or ^Brk.)

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294 <P>

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295 Alternatively, you may use the test file, <tt>test.fc2</tt>,

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296 which has

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297 been provided for use with the File Trace (see below).

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298 Simply run <tt>fc2</tt> with input redirection to take input from

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299 <tt>test.fc2</tt>. At the command prompt, type:

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300 <PRE>

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301 fc2 < test.fc2

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302 </PRE>

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303 <P>

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304

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305 <H2> File Trace </H2>

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306 The File Trace feature of AnaGram allows you to test a

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307 grammar without actually building a parser. This enables you to

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308 completely decouple the debugging of the grammar from the

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309 debugging of the reduction procedures. You can try out test

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310 files before you have written anything more than the

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311 grammar. This allows for very early testing in your projects.

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312 <P>

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313

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314 File Trace allows you to see in fine detail just exactly how

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315 your parser will analyze an input file. A File Trace consists of a

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316 window with various panes so you can see what is going on,

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317 and an interpretive parser which works in the background.

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318 <P>

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319 You can select File Trace from the Action

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320 menu once you have analyzed your grammar. For the <tt>fc2</tt>

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321 example, you will be offered a choice of test files with

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322 extension <tt>.fc2</tt>. A good choice would be <tt>test1.fc2</tt>.

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323 The File Trace window will show a Parser Stack

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324 pane to your left, a Test File pane, which shows you the

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325 input file you are parsing, to your right, and a Rule Stack

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326 pane across the bottom of the window.

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327 <P>

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328 The way the File Trace parser works is this: Initially none of

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329 the test file has been parsed. If you double-click with the

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330 left mouse button at a point in the Test File pane, the parser

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331 parses to that point. The unparsed part of the file will be

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332 colored differently from the parsed part (in the default

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333 color scheme, parsed characters

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334 have a lighter background). To back up the parse to a

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335 previous location, double-click at that spot, or single-click

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336 and press Enter or the Synch Parse button at the bottom of

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337 the File Trace window. To check a file for syntax errors, all

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338 you need to do is to click the Parse File button. If there is

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339 a syntax error, the parse will not advance beyond the error

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340 point. Normally, however, you will probably want to proceed

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341 more deliberately, moving the cursor one character at a

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342 time.

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343 <P>

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344 If you wish to see even finer detail, you may make the

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345 parser work in single step mode. by clicking on Single Step

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346 or pressing Enter. Each time you click on the Single Step

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347 button or press Enter, the parser will perform one parser

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348 action. Note that in its normal configuration, AnaGram

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349 produces parsers that use a number of parser actions more

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350 complex than the traditional shift and reduce actions.

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351 <P>

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352 The Parser Stack pane shows the levels of the parser stack, the

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353 state numbers on the stack and the tokens that have been

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354 recognized so far.

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355 As you advance through the test file, you can see by

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356 looking at the Parser Stack pane how the parser stack changes

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357 as characters are shifted in and reductions occur. The Rule

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358 Stack pane is an alternate view of the parser stack showing

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359 the grammar rules in play at any moment. Notice how the

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360 syntax file window is synched with the Rule Stack.

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361 <P>

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362 If the parse position is not located at the blinking cursor,

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363 the Single Step button will be changed to read "Synch Parse".

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364 Clicking on the button will move the parse position to the

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365 cursor.

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366 <P>

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367 If you now click on tokens at various levels in the Token

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368 Stack, the Test File characters corresponding to these tokens

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369 will be highlighted. You can restart the parse at any level

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370 by double-clicking just preceding the highlight. The Rule

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371 Stack is also synched with the Token Stack and Test File

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372 panes.

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373 <P>

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374 You may interrupt the File Trace at any time to inspect any

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375 other window without interfering with the File Trace.

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376 Whenever you come back to it, you can proceed as though

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377 nothing has happened.

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378 <P>

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379 If you have a long file, a complex grammar, or a (very) slow

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380 computer, it can sometimes take a while for the parse to catch

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381 up with the cursor. If you have a long test file and press

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382 Parse File to move the cursor to the end of the file, the

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383 parser has a lot of computation to do to catch up.

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384 <P>

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385 For further details about the File Trace, please refer to the

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386 AnaGram User's Guide and the on-line documentation.

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387 <P>

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388 <BR>

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389

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390

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391 <H2> FC3 </H2>

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392 <tt>fc3</tt> adds two new features to <tt>fc2</tt>: It uses

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393 floating point

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394 arithmetic, so that it can deal with non-integral values,

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395 and it allows optional white space, including comments, in

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396 the input. In addition, it changes the output format, so

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397 that results are printed in degrees Kelvin, as well as in

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398 Fahrenheit and Celsius.

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399 <P>

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400 The following features of AnaGram are introduced in <tt>fc3</tt>:

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401 <UL>

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402 <LI> Setting the default token type </LI>

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403 <LI> The "disregard" statement </LI>

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404 <LI> The "lexeme" statement </LI>

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405 <LI> Right recursion </LI>

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406 <LI> Default value of a reduction token </LI>

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407 </UL>

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408 <P>

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409

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410 <H3> Floating Point Arithmetic </H3>

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411 To deal with floating point arithmetic, a number of new

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412 productions have been added and two productions have been

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413 changed. Productions P5 and P6 have been changed to define a

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414 "number" in terms of an "unsigned number" instead of an

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415 "integer". Productions P6a, P6b, and P6c define "unsigned

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416 number" in terms of its integer part and its fraction part.

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417 Productions P9 and P10 define the fraction part of the

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418 number. Note that "fraction" is described using right

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419 recursion rather than left recursion. This makes the reduction

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420 procedures neater. Since reduction does not occur until

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421 a rule is complete, note that with right recursion each new

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422 digit causes the stack depth to increase by one. You can

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423 observe this with the File Trace.

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424 <P>

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425 In order to replace integer arithmetic with floating point

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426 arithmetic, statement C3 was added to the configuration

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427 section of the grammar. It declares the default token type,

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428 the type assigned to nonterminal tokens absent a specific

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429 declaration, to be "double". Since we are not interested in

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430 values for "grammar" and "temperature", they have been

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431 explicitly cast to "void".

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432 <P>

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433 Note that production P6a does not have a reduction procedure.

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434 If a rule has no reduction procedure the value of the

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435 reduction token defaults to the value of the first element

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436 in the rule. In this case, the value of "unsigned number",

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437 in the absence of a reduction procedure, is taken to be the

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438 value of "integer".

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439 <P>

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440

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441 <H3> Skipping White Space </H3>

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442 Two statements, C4 and C5, are used to skip over uninteresting

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443 white space in the input to <tt>fc3</tt>. The "disregard" statement

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444 instructs AnaGram to rewrite your grammar in a standard

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445 way so that your parser will skip over any instance of the

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446 "white space" token that occurs between lexemes, or lexical

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447 units, in the input to your parser. Of course, you can use

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448 any token name you wish in a "disregard" statement. You can

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449 even have multiple "disregard" statements and all of the

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450 tokens you specify will be disregarded.

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451 <P>

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452 The "lexeme" statement is used to declare that certain

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453 nonterminal tokens are each to be considered as indivisible

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454 lexical units, or lexemes, from the point of view of lexical

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455 analysis, so that the "disregard" statement is inoperative

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456 inside the nonterminal tokens listed. In this case, statement

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457 C5 simply guarantees that white space will not be

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458 allowed inside a number. All terminal tokens are automatically

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459 lexemes.

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460 <P>

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461 <!--

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462 It would be nice to rewrite this so the example expansion is

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463 vaguely close to syntactically legal.

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464 -->

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465 To make your parser skip white space, AnaGram renames and

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466 redefines the lexemes in your grammar and defines a number

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467 of new tokens. For example, if '+' is a lexeme in your

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468 grammar and your grammar is to disregard "white space",

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469 AnaGram will rename the plus sign token as '+'%. It then

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470 introduces a new production in your grammar as follows:

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471 <PRE>

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472 '+'

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473 -> '+'%, white space?...

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474 </PRE>

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475

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476 This means that a plus sign followed by some white space

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477 will now be treated the same, syntactically, as a plus sign

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478 alone. The percent sign (a degree sign in AnaGram 1.x) is

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479 used to indicate the original, or "pure",

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480 definition of the token.

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481 <P>

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482 Productions P11 and P12 together define what is meant by

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483 white space in this grammar. P11 defines white space to

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484 include blanks and tab characters. P12 includes C style

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485 comments (not nested).

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486 <P>

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487 The white space defined in P11 and P12 does not include

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488 newline characters. There is a good reason for this. The

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489 grammar uses newline characters as delimiters, marking the

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490 end of a "temperature". In order to allow blank lines,

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491 production P1 was modified to make the temperature optional.

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492 <P>

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493 To allow "//" style comments, a new token, "end of line",

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494 defined by production P13, was added. In production P1, '\n'

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495 was then replaced by "end of line".

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496 <P>

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497

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498 <H3> Testing FC3 </H3>

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499 The "test file mask" was changed to use files with the

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500 extension ".fc3" in the File Trace. TEST.FC3 can be used as

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501 input for the File Trace.

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502 <P>

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503 Build and compile <tt>fc3</tt> in the same way as previous versions.

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504 When you run it, try using numbers with decimal fractions.

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505 Try typing blanks in various places to see how the parser

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506 deals with them. Try redirecting input from <tt>test.fc3</tt>.

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507 <P>

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508

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509

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510 <H2> FC4 </H2>

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511 <tt>fc4</tt> illustrates a shift-reduce conflict in a grammar. You

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512 should probably skip this example until you encounter a

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513 shift-reduce conflict in one of your own grammars. In the

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514 meantime, skip ahead to <tt>fc5</tt>.

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515 <P>

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516 The following features of AnaGram are introduced in <tt>fc4</tt>:

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517 <UL>

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518 <LI> Conflicts window </LI>

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519 <LI> Auxiliary Windows menu </LI>

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520 <LI> State Definition window </LI>

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521 <LI> Expansion Chain window </LI>

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522 </UL>

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523 <P>

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524 In <tt>fc3</tt>, the output was changed to provide results in degrees

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diff changeset

525 Kelvin, as well as in Fahrenheit and Celsius. In <tt>fc4</tt>, a

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diff changeset

526 production, P3a, is added to accept input in degrees Kelvin.

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diff changeset

527 Since there is no such thing as a negative temperature on

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diff changeset

528 the Kelvin scale, it seemed appropriate to require that the

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529 temperature be an unsigned number. This, however, caused a

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530 conflict, i.e. an ambiguity, in <tt>fc4</tt>. In fact, it caused four

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531 conflicts to be diagnosed, all of which have a common

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532 source.

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533 <P>

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534

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diff changeset

535 <H3> Finding a Conflict </H3>

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diff changeset

536 If you run AnaGram and analyze <tt>fc4</tt> you will find that

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537 AnaGram finds conflicts in the grammar. To determine the nature

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538 of the conflicts, you should first open the Conflicts

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539 window. The Conflicts window is available via the Browse Menu

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540 or a Control Panel button.

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541 <P>

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542 The first thing you see is that there are conflicts in

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543 states S005 and S025. In each state, one conflict occurs

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544 because a decimal point can either be shifted, in accordance

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545 with rule R021, or it can reduce rule R014, an empty rule,

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diff changeset

546 or null production. The other conflict occurs because a

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547 decimal digit can either be shifted, in accordance with rule

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548 R022, or it can reduce rule R014, the same rule that gives

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549 trouble with the decimal point.

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550 <P>

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551 The first step in understanding the conflict is to see rules

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552 R014, R021, and R022 in context. The Conflicts window is

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553 synchronized with the syntax file window. Arrange these

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554 windows so you can see them both at once.

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555 Then, in the Conflicts window, move the cursor bar up and

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556 down. In the syntax file window, the cursor will move

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557 between productions for number, unsigned number and integer.

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558 <P>

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559 Although it is possible to recognize rules R021 and R022 in

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560 the grammar, there is no explicit null production in the

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561 grammar. To find out for sure what rule R014 is, pop up the

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562 Rule Table (listed in the Browse menu) and look for R014. It

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563 turns out that R014 is the null production that corresponds

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564 to an optional plus sign, written '+'? in the grammar.

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565 <P>

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566 To get a better idea of what is going on, it is worthwhile to

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567 find out what the parser is expecting to see in states S005

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568 or S025. To find out, click the right mouse button in the

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569 Conflicts window on any line describing a state S005

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570 conflict to pop up the Auxiliary Windows menu. Select State

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571 Definition to find out what state S005 is all about. It

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572 seems that state S005 occurs when the parser has skipped

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573 over the initial white space and is about to begin dealing

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574 with the actual input. But, looking at this, it is still not

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575 clear why a decimal digit or a decimal point is ambiguous.

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576 The Expansion Chain windows for rules R021, R022 and R014

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577 will show how these rules are derived from the

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578 characteristic rule for state S005.

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579 <P>

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580

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581 Return to the Conflicts window. Click the right mouse button

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582 on rule R021, the rule that expects the decimal digit,

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583 to pop up the Auxiliary Windows menu. Select

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584 Expansion Chain. The Expansion Chain window shows how rule

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585 R021 derives from the characteristic rule for the state.

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586 Each line in this window is a grammar rule produced by the

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587 marked token in the rule on

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588 the previous line.

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589 <P>

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590 Now return to the Conflicts window, and get the Expansion

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591 Chain window for rule R014. Rearrange the windows on the

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592 screen so you can compare the Expansion Chain windows for

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593 rules R014 and R021. Note that rule R014 derives from the

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594 production

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595 <PRE>

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596 temperature

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597 -> number, 'c' + 'C'

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598 </PRE>

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599 and rule R021 derives from the production

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600 <PRE>

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601 temperature

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602 -> unsigned number, 'k' + 'K'

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603 </PRE>

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604 <P>

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605 It is now possible to see the nature of the conflict. On the

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606 one hand, if the input is a supposed to be a Kelvin

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diff changeset

607 temperature, the parser can go right ahead accumulating a

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608 number. On the other hand, if the input is supposed to be a

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609 Celsius number, the parser has to first acknowledge the

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610 optional plus sign.

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611 <P>

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612 It is the nature of LALR parsers that they can keep track of

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613 many threads of possible parses simultaneously as long as

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614 they don't have to do any reductions. When they come to the

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615 end of a rule, however, they are forced to decide whether

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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diff changeset

616 the rule has been successfully matched. In this case, the

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617 parser is at the end of a null production which arises from

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618 the virtual production <CODE> '+'? </CODE> in P6 and is forced to decide

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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diff changeset

619 whether this null production has been matched. The conflict

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620 diagnostics discussed above say that if the next token is a

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621 digit or a decimal point, the parser cannot decide between

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622 several possibilities. That is, it cannot decide whether or

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diff changeset

623 not it has seen an elided plus sign. In effect the parser is

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624 being required, because of the null production, to make a

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625 premature decision as to whether a Kelvin or Celsius

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626 temperature is present in the input.

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627 <P>

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628 The conflicts can be eliminated by rewriting the grammar so

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629 the parser will not come to the end of a rule and be forced

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630 to choose among the several threads of the parse until it

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diff changeset

631 encounters the determining letter 'f', 'c', or 'k'.

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632 <P>

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633 Two ways to remove the conflict are illustrated. The first is

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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634 found in FC4A. In this grammar, production P6 has been

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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635 replaced with two productions, P6x and P6y. This is a

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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diff changeset

636 standard method of rewriting a grammar to eliminate null

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637 productions. If you analyze <tt>fc4a</tt>, you will find that it no

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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638 longer has a conflict, so this solves the problem.

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639 <P>

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diff changeset

640 However, if you look at the <tt>fc4a</tt> grammar closely, you will

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641 notice that +23.7K is not acceptable input, although common

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642 sense suggests that you ought to be able to use a plus sign

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643 on Kelvin temperatures. <tt>fc4b</tt> shows another way to fix the

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diff changeset

644 grammar which deals with this quibble. In this grammar,

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diff changeset

645 production P3a has been modified to allow an optional plus

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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diff changeset

646 sign before a Kelvin temperature. If you analyze <tt>fc4b</tt>, you

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diff changeset

647 will find that this change also solves the problem.

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diff changeset

648 <P>

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diff changeset

649 In both these instances, the technique used to resolve the

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diff changeset

650 conflicts was to rewrite the grammar so that there are no

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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diff changeset

651 differences between constructs upstream of the point where

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diff changeset

652 they diverge. Another way to put it is this: In the original

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diff changeset

653 grammar Kelvin temperatures were distinguished from

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diff changeset

654 Fahrenheit and Celsius not only by the 'K' suffix, but also by the

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diff changeset

655 optional plus sign. The essence of both fixes to the problem

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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diff changeset

656 is to remove this distinction.

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657 <P>

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diff changeset

658 Other AnaGram windows available from the Auxiliary Windows

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659 popup menu for the Conflicts window such as Rule Derivation, Token

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diff changeset

660 Derivation, Conflict Trace and Problem States are helpful in

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diff changeset

661 tracking down conflicts. See the help messages and your

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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diff changeset

662 AnaGram User's Guide for further details.

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663 <P>

13d2b8934445 Import AnaGram (near-)release tree into Mercurial.

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664

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diff changeset

665 <H3>Testing FC4A and FC4B </H3>

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diff changeset

666 Build and compile <tt>fc4a</tt> and <tt>fc4b</tt> in the

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diff changeset

667 same way you built

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diff changeset

668 previous versions. When you run the parsers, try using

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diff changeset

669 Kelvin temperatures with and without leading plus signs.

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diff changeset

670 <P>

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671 The "test file mask" was changed to use files with the

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672 extension ".fc4" in the File Trace. <tt>test.fc4</tt> can be

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673 used as

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674 input either for the parsers themselves or for the File

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675 Trace.

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676 <P>

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677

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678

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diff changeset

679 <H2> FC5 </H2>

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diff changeset

680 <tt>fc5</tt> illustrates the use of an event driven parser. The

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681 grammar is essentially the same as for <tt>fc4b</tt>. The primary

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682 difference is in the method of providing input to the

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683 parser. The following features of AnaGram are introduced in

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684 <tt>fc5</tt>:

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685 <UL>

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686 <LI> event driven parser </LI>

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687 <LI> embedded C </LI>

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688 <LI> main program </LI>

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689 <LI> initializing and calling the parser </LI>

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690 </UL>

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691

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692 Statement C6 in the configuration section causes AnaGram to

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693 build an event driven parser. An event driven parser is

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694 first explicitly initialized and then called once for each

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695 input unit.

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696 <P>

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697 A small main program has been included in a block of

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698 embedded C at the end of the file. This program calls the

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699 initializer and then reads characters from <CODE>stdin</CODE> and passes

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700 them on to the parser. Previous <tt>fc</tt> programs did not

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701 include a

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702 main program, but relied on AnaGram to create one. However,

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703 AnaGram does not automatically create a main program for

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704 parsers which are event driven, use pointer input, or have

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705 any embedded C. Therefore a main program is necessary in

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706 this syntax file.

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707 <P>

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708 Note that the default names for the initializer and parser

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709 are <CODE>init_fc5</CODE> and <CODE>fc5</CODE> respectively.

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710 Only event driven parsers

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711 require that the user explicitly call the initializer

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712 function.

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713 <P>

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714 In addition, a global constant, "zero", was defined in the

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715 embedded C to provide the value of absolute zero, and the

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716 reduction procedures were modified to refer to "zero"

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717 instead of the explicit value.

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718 <P>

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719 This illustrates an important point about the C parser file

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720 that AnaGram builds: All blocks of embedded C precede the

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721 reduction procedures, so that the reduction procedures can

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722 access all variables and definitions included in embedded

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723 C, no matter where they are located in the file.

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724 <P>

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725

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726 <H3>Testing FC5 </H3>

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727 Since <tt>fc5</tt> uses the same grammar as <tt>fc4</tt>,

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728 you can use the same

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729 test files for <tt>fc5</tt> as for <tt>fc4</tt>.

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730 </P>

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731

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732 <BR>

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733

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734 <IMG ALIGN="bottom" SRC="../images/rbline6j.gif" ALT="----------------------"

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735 WIDTH=1010 HEIGHT=2 >

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736 <P>

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737 <IMG ALIGN="right" SRC="../images/pslrb6d.gif" ALT="Parsifal Software"

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738 WIDTH=181 HEIGHT=25>

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739 <BR CLEAR="right">

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740 <P>

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741 Back to <A HREF="../index.html">Index</A>

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742 <P>

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743 <ADDRESS><FONT SIZE="-1">

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744 AnaGram parser generator - examples<BR>

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745 Fahrenheit-Celsius Converter<BR>

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748 </FONT></ADDRESS>

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749

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750 </BODY>

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751 </HTML>

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752

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

annotate doc/misc/html/examples/fc.html @ 0:13d2b8934445