> Norman Ramsey wrote: > > > compile1 :: (Builder b box) => t -> Name -> Ir.ANF -> b t > > compile1 f x body = do env <- compile body empty > > wire (Arg W) (env x) > > return f > > class (Monad b) => Builder b box where > > wire :: Source box -> Sink box -> b () > > This program is rejected by GHC... > > He continued, [paraphrase] however, compile1 is accepted if the signature is > removed. Furthermore, the inferred signature seems identical to the > one given above. > > That is not a bug... > > What to do? If applicable, add a functional dependency ... > > Or, one may use the local type variable to the same end > > > compile1 :: forall b t box. (Builder b box) => t -> Name -> Ir.ANF -> b > > t compile1 f x body = do env <- compile body empty > > wire ((Arg W)::Source box) (env x) > > return f > > the explicit `forall' binder is required.
This suggestion, I like. I have always hated that ML and Haskell leave the foralls implicit. Bad design. To be sure I understand: the reason the explicit forall is required is to bring 'box' into scope so it can be used in the type constraint on (Arg W)? Norman _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
