At 16:32 +0100 2002/10/17, Simon Marlow wrote:
So I wonder if somebody may want to make an attempt to produce such skeleton files for Haskell. Bison has now not only an LALR(1) parser algorithm, but also a GLR parser, and more is to come.
Note that Happy has support for some Haskellish things which you won't get if you use bison to generate Haskell. For example: type signatures on productions, and support for threading a monad around the parser.
I am not sure what these type signature are: But Bison has a typing feature currently only used with the implementation of unions. It is easy to tweak to become only a typing feature (not tied to C union in implementation). By macros, one can then write out a suitable form of the semantic variables to extract the correct typing. I am not sure what exactly this "threading a monad" around the parser means: But under C++, I am now wrapping C++ namespaces around my parser. I have suggested that Bison should get a construct %define <name> <definition> producing a suitable macro handed over to M4. Thus, I should be able to write %defined namespace <name> and exploit that to create a suitable namespace around the parser. Such a procedure is sufficiently general that it ought to be able to handle your monad wrapping as well. -- But one can only know for sure by actually trying, and the feedback from such a try might be interesting.
Nevertheless, doing this sounds entirely feasible. The parser tables generated by bison are very similar to those generated by Happy (I peeked at bison's source when I wrote the table-generation code in Happy), so looking at Happy's LALR(1) machine might be a good place to start.
Then interaction between Happy and Bison might turn out to be interesting. The Bison people may also want parser generator sources in other languages, functional like LISP (Scheme), SML, as well as others. I am not myself actively programming in Haskell now, so that is one reason I posted it. I should have mentioned that more info about Bison can be found on its mailing lists: help-bison@gnu.org http://mail.gnu.org/mailman/listinfo/help-bison bug-bison@gnu.org http://mail.gnu.org/mailman/listinfo/bug-bison Hans Aberg