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From: ramsey@ncoast.UUCP
Newsgroups: comp.compiler,comp.lang.c
Subject: 'C', is it's grammar context sensitive ?
Message-ID: <FooBarg23.164905.10261@NCoast.ORG>
Date: 27 Aug 90 07:37:34 GMT
Organization: North Coast Public Access *NIX, Cleveland, OH
Lines: 57


	Hello again ! This question is directed towards the 'C' and compiler
gurus out there. I was studying the grammar for the 'C' language and I couldn't 
help but notice that for declarations the grammar is context sensitive.
Look at this here:

declaration: declaration-specifiers init-declarator-list_opt;
declaration-specifiers: 
	storage-class-specifier declaration-specifiers_opt
	type-specifier declaration-specifiers_opt
	type-qualifier declaration-specifiers_opt
type-specifier: one of
	void char short int long float double signed unsigned 
	struct-or-union-specifier enum-specifier typedef-name
typedef-name: IDENTIFIER

Since the 'typedef-name' is an identifier is impossible to determine that
it is a type defintion without looking at the context. I guess that one could
do a pre-scan of the source code and build typedef trees but I thought that
'C' was context free grammar. If you try to build a parser using the above 
grammar, which I did, a declaration tree for following grammar might derive:

sometype  id;

                                  declaration
                                  /         \
                 declaration-specifiers    init-declarator-list
                  /                                         \
         type-specifier                                     NULL
         /            \
typdef-name          type-specifier
     |                          \
IDENTIFIER = 'sometype'   typedef-name
                               |
                          IDENTIFIER = 'id'


Instead of:

                                  declaration
                                  /         \
                 declaration-specifiers    init-declarator-list
                  /                        /                  \
         type-specifier          init-declarator             NULL
         /          \                   |                      
typdef-name        NULL             declarator
     |                              /        \    
IDENTIFIER = 'sometype'        pointer      direct-declarator
                                 |              | 
                                NULL          IDENTIFIER = 'id'


Do you see point? I hope you do. Like I said before the solution to this
problem, I believe, is to do a pre-pass to collect typedef definitions or
just rearrange the grammar some-kind of adhoc way. I think that the prescan
idea is best best it keeps the grammar simple and easy to follow. What do
use guys think ?