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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 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
2
3 <HTML>
4 <HEAD>
5 <TITLE>C Parsers - Macro preprocessor and C Parser </TITLE>
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19 <A HREF="index.html">Macro preprocessor overview</A>
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25 <P>
26
27 <H1>C Parsers - Macro preprocessor and C Parser </H1>
28
29 <IMG ALIGN="bottom" SRC="../../images/rbline6j.gif" ALT="----------------------"
30 WIDTH=1010 HEIGHT=2 >
31 <P>
32 <BR>
33
34 Two C grammars are provided with this example: <tt>jrc.syn</tt> is a
35 translation of a <tt>yacc</tt> grammar for C created by James A.
36 Roskind. <tt>krc.syn</tt> is a grammar adapted from Kernighan and
37 Ritchie, Section A13.
38 <P>
39 Both grammars use semantically determined productions to
40 distinguish between typedef names and identifiers, however,
41 neither grammar has been adapted to take advantage of this
42 capability to resolve many of the problems associated with
43 typedef names.
44 <P>
45 In order to parse simple examples successfully, it was
46 necessary to create a rudimentary capability to recognize
47 typedef names. Such capabilities were incorporated into each
48 grammar. Note that the scope handling is inadequate for
49 production use.
50 <P>
51 In <tt>jrc.syn</tt>, the typedef token causes a flag to be set. When
52 the identifier in a declaration is encountered, the flag is
53 interrogated. The complication is the possible interposition
54 of field names within a struct or union which could be
55 inadvertently marked as typedef names. To avoid this, the
56 flag is stored on encountering a struct or union and
57 restored when the danger is past.
58 <P>
59 In <tt>krc.syn</tt>, the treatment of typedefs is marginally less
60 inelegant. Storage class attributes are accumulated in a bit
61 mask. As identifiers are encountered in the declaration
62 statement they are pushed onto a multilevel stack, <tt>id_stack</tt>.
63 When struct or union declarations are encountered, the level
64 of the id_stack is incremented. When the danger is past, the
65 level is decremented so that identifiers stacked in the
66 course of parsing the struct or union are discarded.
67 Eventually, when the statement is complete, all the
68 identifiers that have been found are popped from <tt>id_stack</tt>
69 and given the appropriate storage class attribute.
70 <P>
71 Both grammars are set up so that the name of the parser is
72 <tt>cc()</tt>.
73 Each
74 syntax file contains member function definitions for the
75 class <tt>c_parser</tt>. They are identical except for the
76 initialization of the typedef logic. The definition of the
77 class <tt>c_parser</tt> is found in <tt>MPP.H</tt>.
78 <P>
79 <B>Note:</B> Until AnaGram 2.40, the parsers were set up
80 so both would emit the files <tt>cc.cpp</tt> and
81 <tt>cc.h</tt>. This caused problems for AnaGram 2.40's more
82 automated build and test system. As of this writing,
83 <tt>krc.syn</tt> is used by default; to use <tt>jrc.syn</tt>
84 you must change the <tt>#include</tt> near the top of
85 <tt>mpp.h</tt> to include <tt>jrc.h</tt>. With luck, this
86 annoyance will be cleared up in a future release.
87 <P>
88 It should be noted that the KRC grammar has at least one
89 bug. It will not recognize function declarations of the
90 form:
91 <PRE>
92 foo(int);
93 </PRE>
94 It will, however, recognize
95 <PRE>
96 int foo(int);
97 </PRE>
98 This problem appears to be inherent in the grammar published
99 in K &amp; R.
100 <P>
101 <BR>
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118 AnaGram parser generator - examples<BR>
119 C Parsers - Macro preprocessor and C Parser <BR>
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