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Date: -- (:)
From: Jean-Christophe Filliatre <Jean-Christophe.Filliatre@l...>
Subject: Re: [Caml-list] yacc style

Erik de Castro Lopo writes:
 > skaller <skaller@users.sourceforge.net> wrote:
 > > On Fri, 2005-01-28 at 08:39, Erik de Castro Lopo wrote:
 > > >
 > > > Yes, normally the parser generates a parse tree which is then
 > > > passed to the semantic analyser for semantic checking.
 > > 
 > > Unfortunately this is useless in the common case
 > > of needing to parse C.
 > 
 > Could you give a example?

When parsing C, the lexer  must produce different tokens for variables
identifiers  and  types identifiers,  otherwise  you may  misinterpret
things  like "a  * b"  (is it  the  declaration of  a pointer  b or  a
multiplication?) or casts. The following piece of code is illustrating
the difficulty:

======================================================================
int a, b;
typedef int t, u;
void f1() { a * b; }
void f2() { t * u; }
void f3() { t * b; }
void f4() { int t; t * b; }
void f5(t u, unsigned t) {
  switch ( t ) {
  case 0: if ( u )
    default: return;
  }
}
======================================================================

The  solution  is  to  have  the  parser  modifying  the  lexer  while
parsing. This is quite ugly in practice. The CIL framework includes a
full C parser written in ocaml, so you can get there one possible way
of handling this issue; see http://manju.cs.berkeley.edu/cil/

Hope this helps,
-- 
Jean-Christophe Filliātre (http://www.lri.fr/~filliatr)