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Import AnaGram (near-)release tree into Mercurial.
author David A. Holland
date Sat, 22 Dec 2007 17:52:45 -0500
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1 % This file was converted by WP2LaTeX version 2.99
2 % (and modified a lot afterwards)
3
4 %\baselineskip=2.00ex
5 %
6 %\headtext{\evenpages}{
7 %\thepage AnaGram User's Guide
8 %}
9 %\foottext{\allpages}{
10 %\strut\hfill \today{}
11 %}
12 %\headtext{\oddpages}{
13 %Chapter 1\hfill Introduction\thepage
14 %}
15 %\vspace{2.55cm}%
16 %\begin{flushright}
17 %
18 %\section{{ Chapter 1
19 %Introduction to AnaGram}}
20 %\end{flushright}
21
22 \chapter{Introduction to AnaGram}
23
24 AnaGram is a software development tool which brings the power of
25 syntax directed parsing to the C or C++ programmer. AnaGram provides
26 a rule-based, non-procedural system for dealing with input to computer
27 programs.
28
29 AnaGram is a completely new LALR parser generator with a powerful
30 notation for representing context free grammars. A flexible,
31 interactive environment combined with powerful debugging capabilities
32 and language extensions make it easy to incorporate syntax directed
33 parsing in your programs. AnaGram makes it possible for you to reap
34 the benefits of syntax directed parsing on all of your projects, big
35 and small.
36
37 Syntax directed parsing has long been recognized as the most powerful
38 technique available for interpreting program input. Up to now, the
39 tools available to the software developer to support this technique
40 have been primitive and hard to use, suitable mainly for compilers and
41 other large projects. AnaGram was specifically designed to make
42 syntax directed parsing accessible to the software developer for
43 everyday use.
44
45 Few portions of a program are more prone to errors than the logic that
46 deciphers the input to the program. To interpret its input a program
47 usually needs many flags and switches, many tests, and a lot of
48 conditional code. Of necessity such a program has many paths and many
49 opportunities to go awry. Such code is hard to write, hard to
50 document, hard to debug and hard to maintain.
51
52 With AnaGram, you can completely separate the analysis of input from
53 the processing of data. Instead of writing a detailed procedure for
54 interpreting input, you write a {\it description} of that input using
55 an adaptation of
56 % noindex
57 Backus-Naur Form, or BNF.
58 AnaGram builds for you,
59 based on your description, a procedure to interpret your input. All
60 those tests, all that conditional code, all those flags and switches
61 vanish. In a convenient way you can attach, to the procedure, code to
62 process the data once it is identified in the input stream. Your
63 input processing now takes on the aspect of a rule-based,
64 non-procedural system.
65
66 There are many benefits to this approach. Your program is easier to
67 understand. It is easier to debug. It is easier to extend and
68 maintain. A large project can be more easily divided up among the
69 members of your team. The description, or grammar, of your input can
70 serve as solid and reliable documentation. You will also find that it
71 becomes much easier to re-use code on other projects, because the data
72 processing is cleanly separated from the parsing, or input analysis.
73
74 These benefits are now available because AnaGram, in addition to
75 implementing the basic algorithms of an LALR parser generator,
76 provides powerful new features that make syntax directed parsing a
77 practical reality. Here is a summary of some of the more important
78 features of AnaGram:
79
80 \paragraph{Interactive File Trace.}
81 An online
82 % noindex
83 \agwindow{File Trace} function lets you run test files through your
84 grammar interactively. You can see how your parser will interpret
85 them. You can see the contents of the parse stack. You can see the
86 grammar rules that are partially matched at any stage in the parse.
87 You can back up the parse to any point and try again. You can go
88 through a test file in single step mode, one character at a time, or
89 simply parse the whole file to see if it has any errors. While
90 interpreting your grammar and parsing your file, AnaGram will count
91 the number of times each grammar rule is matched and give you a report
92 so you can assess the thoroughness of your testing.
93
94 \paragraph{Grammar Trace.}
95 The
96 % noindex
97 \agwindow{Grammar Trace} is another feature which allows you to
98 inspect the workings of your parser interactively. It is particularly
99 suited for dealing with ``what if?'' questions. You can work through
100 a parse at whatever level of detail is necessary to see how an error
101 arises, to see the nature of an ambiguity, or simply to gain
102 confidence in the way the parser works. In case of certain types of
103 errors, AnaGram will provide pre-built grammar traces to illustrate
104 the problem.
105
106 \paragraph{Other Debugging Tools.}
107 AnaGram provides a number of debugging tools that can help you get
108 your program up and running on schedule. In particular, AnaGram has
109 powerful tools for identifying ambiguities in your grammar. AnaGram
110 also has coverage analysis facilities to help you ascertain the
111 effectiveness of your test suites.
112
113 When AnaGram analyzes a grammar, it creates numerous tables describing
114 various aspects of the grammar. To facilitate inspection of these
115 tables, AnaGram has an interactive interface to enable you to find
116 quickly any problems in your grammar. An extensive, on-line help
117 system provides quick online answers to the questions you have about
118 AnaGram.
119
120 \paragraph{No Lexical Scanner Required.}
121 \index{Lexical scanner}
122 When you use AnaGram, you seldom have to use a ``lexical scanner'', or
123 input processor, written in still another programming language, to
124 ``tokenize'' character-based input for your parser. Instead, you can
125 specify {\it all} the details of the input stream directly in your
126 grammar in a natural way. If those details need to be changed, you
127 can make all the changes in one place and rebuild your parser without
128 having to deal with a cumbersome lexical scanner interface. AnaGram
129 accomplishes this by providing a notation that allows you to specify
130 keywords and character sets simply and intuitively. AnaGram also
131 provides options for selectively ignoring white space or other
132 uninteresting characters in your input.
133
134 On the other hand, if you already have a lexical scanner, or some
135 other data source, you can interface it cleanly and simply to a parser
136 AnaGram generates. If the nature of your problem requires a lexical
137 scanner, or multi-stage parsing, you can use AnaGram for each level of
138 parsing.
139
140 \paragraph{Flexible Interfacing.}
141 AnaGram provides numerous ways for you to interface your parser to the
142 rest of your program. Since you can even configure a parser to work
143 in an event driven mode, you can use AnaGram very effectively to deal
144 with the new programming styles required by modern window based
145 operating systems.
146
147 AnaGram provides new notation for linking data to your processing
148 routines. Symbolic hooks tie syntactic constructs directly to your C
149 or C++ code. The processing routines are easier to write and to
150 modify. You can also modify your grammar without having to alter your
151 data processing routines.
152
153 \paragraph{Virtual Productions.}
154 AnaGram provides a powerful, intuitive shorthand notation to help you
155 to describe many commonly occurring syntactic forms, such as optional
156 elements, lists, and simple sets of options.
157
158 \paragraph{Semantic Control over Syntactic Analysis.}
159 Extensions to the basic algorithms for developing LALR parsers allow
160 you to exert semantic control over syntactic processing by using a new
161 feature called ``semantically determined productions''.
162
163 \paragraph{Precise Control over White Space.}
164 Convenient attribute statements allow you to skip white space and
165 comments where they are meaningless, but recognize them where it
166 matters.
167
168 \paragraph{Easy Configuration.}
169 An extensive set of configuration switches and parameters allow you to
170 configure both AnaGram and the parsers you build to your precise
171 requirements. Wherever AnaGram provides options, it also provides
172 sensible defaults, so that you can ignore most switches and parameters
173 until you need the capability they control.
174