Path: utzoo!mnetor!uunet!husc6!bbn!rochester!PT.CS.CMU.EDU!IUS1.CS.CMU.EDU!edw
From: edw@IUS1.CS.CMU.EDU (Eddie Wyatt)
Newsgroups: comp.lang.c
Subject: Re: ambiguous why?
Message-ID: <1320@PT.CS.CMU.EDU>
Date: 5 Apr 88 17:02:24 GMT
References: <1303@PT.CS.CMU.EDU> <22997@bbn.COM>
Sender: netnews@PT.CS.CMU.EDU
Organization: Carnegie-Mellon University, CS/RI
Lines: 26

> > 	*a+=*b;
> > 
> 
> K&R A.17 talks about earlier versions of C which used the form "=op"
> instead of "op=".  Most(?) compilers still try to detect the old form
> and issue a warning.  In my opinion this causes headaches more than it
> catches obsolete code.  Anyway, the compiler wasn't sure if you wanted
> "addition assignment" (+=) or the old multiplication assignment (=*) so
> it complained.  Putting a space after the "=" fixes it:

  This doesn't answer my question.  I am familiar with the old
syntax for operand assignment.  I understand that without some sort of
lexer rule, the above is ambiguous.  However, I thought that a
rule existed that should disambiguated this statement.  In particular,
I do believe a rule exist such that you choose the largest token
posible as you scan left to right.  That is why the statement a+++b is
not ambiguous (optional read a++ + b).

   If what you wrote about the tokenization of +=  (two separate tokens + =)
is correct then the above statement is ambiguous at the parsing level.
In which case I could understand there not existing a disambiguating rule.


-- 

Eddie Wyatt 				e-mail: edw@ius1.cs.cmu.edu