Re: [Caml-list] LL, LR, and camlp4 (was Re: syntax change)

[Xavier Leroy <xavier.leroy@inria.fr>]

> My question is just why did you hand-write the parser, rather than
> using a tool like yacc?  Was it because of the extensibility and hooks
> you needed in camlp4 and there's no way to make an extensible
> generated parser?

Yacc-generated parsers (LALR automata) are certainly not extensible --
or at least not without having to recompute most of the automata at
each extension.

> Are parser generators not all they're cracked up to be?  If so, why
> does caml use yacc?

Like all tools, parser generators work well for what they've been
designed to do.  In the case of Yacc, it works well for fixed grammars
(non extensible) of a certain kind (LALR(1) plus precedences for
disambiguation).  

The Caml compilers (OCaml, Caml Light, and even the original
LeLisp-based Caml) use Yacc-generated parsers because that's the
technology we had available at the time they were written, and it
works relatively well -- some efforts are required to disambiguate the
grammar, but at least Yacc tells you where the ambiguities are.

- Xavier Leroy
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