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Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!rochester!pt.cs.cmu.edu!andrew.cmu.edu!bobg+
From: bobg+@andrew.cmu.edu (Robert Steven Glickstein)
Newsgroups: comp.unix.questions,comp.lang.c
Subject: Yacc probs w/ANSI-C
Message-ID: <UYbhqrq00Vsn43xmA3@andrew.cmu.edu>
Date: 21 Jun 89 00:13:43 GMT
Organization: Information Technology Center, Carnegie Mellon, Pittsburgh, PA
Lines: 38


I've written a parser for ANSI-C using YACC (adhering strictly to the
grammar given in K&R, second edition) that doesn't work.  Despite the
claim in section A13 that "this grammar is acceptable to the YACC
parser-generator"(modulo some changes, which I've made), it in fact is
not; it's not even LR(1).  I get syntax errors in which the parser can't
decide if it's seeing a function-definition or a declaration (while
working on an external-declaration).  Here's the very beginning of the
grammar:

    file ::= external-declaration | file external-declaration
    external-declaration ::= function-definition | declaration
    function-definition ::= opt-declaration-specifiers
        declarator opt-declaration-list compound-statement
    declaration ::= declaration-specifiers
        opt-init-declarator-list ';'

Now consider the input

    extern struct foo bar[];

Every token up to (and including) the ']' represents a legal sequence to
begin either a function-definition or a declaration.  My parser chooses
to begin parsing this as a function-definition, and it barfs when it
sees a ';' instead of a compound-statement.  On the other hand,

    struct foo *bar() {}

is also legal for both function-definitions and declarations (up to the
')'), but the parser chooses to parse this as a declaration, and barfs
when it sees a '{' instead of a ';'.

Can any YACC gurus advise me on how to proceed?  I will gladly mail you
a copy of my YACC source if you can take a look at it.


Thanks,
-Bob Glickstein