Re: LR (k) vs. LALR

"Tim Bauer" <tbauer@cadrc.calpoly.edu> writes:


> > [Some grammars are easier to express with more than one token of lookahead.
> > You can rewrite gramars to LR(1), but sometimes at the cost of huge and
> > ugly bloat. -John]
>
> Didn't Knuth prove that any LR(k) grammar can be rewritten to LR(1), albeit
> at a potential exponetial increase in the parse tables (number of distinct
> parse items).
> However, does this extend to an LALR(k) conversion to LALR(1)?


Every language for which a LR(1) grammar LR(1) exists has also an
LALR(1) grammar. (Search for the archive of this group, I started a
thread on the subject).


> > I have a grammar that requires more than one token of look ahead,
> > is there any way that it could be solved using yacc or Bison?
>
> I do have a suggestion here. I typically see compilers/interpreters
> make some syntactic concessions and offload extra checking to the
> semantic checker.


The major raison I do this is that it is easier to give good error
message and have some good error recovery.


Yours,


--
Jean-Marc

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