[Haskell-cafe] Re: re: generics and grammars

Chung-chieh Shan ccshan at post.harvard.edu
Thu Dec 13 18:03:58 EST 2007

Greg Meredith <lgreg.meredith at biosimilarity.com> wrote in article <5de3f5ca0712120917h7864fe39m2c6a2c6c379437e7 at mail.gmail.com> in gmane.comp.lang.haskell.cafe:
> Thanks for the references! Have two-level types been applied to parser
> generation?

Hrm, I'm not sure what kind of application you have in mind, so I
suppose the answer is that I'm not aware of any application. (:
I suppose that the parser for the type-level fixpoint of a type
constructor is the term-level fixpoint of a parser constructor.
Unfortunately "data Fix f = Fix (f (Fix f)) deriving Read" doesn't work
in Haskell, because there's no way to express the constraint that the
type "f a" is an instance of Read whenever the type "a" is.  However,

    Valery Trifonov. 2003.  Simulating quantified class constraints.
    In Haskell workshop, 98-102.

This discussion also reminds me of

    Ralf Hinze. 2000.  A new approach to generic functional programming.
    In POPL, 119-132.


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