On Mon, Jan 22, 2007 at 11:34:32PM +0100, Benjamin Franksen wrote: > I would be interested whether you can not only /check/ well-typedness, but > also /establish/ it, i.e. is it possible to have the input to the > type-checker be an /untyped/ representation (such as obtained by parsing a > program in text form) and the output be a typed one (or else a type error)? > > From my very limited understanding of these issues I would say it is not > possible, neither with type-classes nor with G[AR]DTs because it would mean > the return type of the function 'typecheck' would have to vary depending on > the input data, hence you'd need a genuinely dependent type system for such > a feat.
You can do this with existential types and with higher-rank polymorphism (the latter if you write your parser in CPS). Best regards Tomasz _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
