Re: [QUERY] A "ignorant newbie" question about compiler-writing.

cartegw@humsci.auburn.edu (Gerald W. Carter) writes:


|> > > > even Pascal requires some hacks.
|> >
|> > > In my recollection, only in parsing (0.1 vs 0..1), though "with"
|> > > clauses can be a bit tricky regarding sematic analysis. (though I may
|> > > be wrong, as I haven't worked on a pascal compiler for about 7 years).
|>
|> > Actually, the specific case I was thinking about was the distinction
|> > between an assignment statement and a procedure call. I actually think
|> > that you could write an LR grammar which would work even if the scanner
|> > returned user symbol in both cases, but it would be complicated. The
|> > usual solution is for the scanner to do a symbol table lookup, and
|> > return a different token if the symbol is defined as a procedure. In
|> > short, a hack.
|>
|> I don't believe that the symbol table lookup is neccessary. For example
|>
|> ----------------------------------------
|> statement : assignment
|> | procedure_call
|> ;
|>
|> assignment : variable BECOMES expression /* must test for func_ident */
|> ;
|>
|> procedure_call : ident actual_params
|> ;
|> ----------------------------------------


It's certainly doable (I think), but it is definitly more complicated
than this. Consider that the left hand side of an assignment is not
just a variable. It can be any arbitrary expression, including a call
to a function which returns a pointer, e.g.:


        fnc( arg1 , arg2 )^ := someValue ;


So you will have to develop the grammar so that things like "ident '('
... ')'" reduce to a commun term legal both on the left side of
assignment *and* as a procedure call.


This seems a bit artificial to me, and while theoretically, it is nice,
I think that I'd go with the hack myself, as being easier to maintain
and to understand.
--
James Kanze +33 (0)1 39 55 85 62 email: kanze@gabi-soft.fr
GABI Software, Sarl., 22 rue Jacques-Lemercier, 78000 Versailles, France
--

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