AllowAmbiguousTypes at this point only extends to signatures that are
explicitly written.
This would need a new "AllowInferredAmbiguousTypes" or something.
On Sat, Oct 12, 2013 at 5:34 PM, adam vogt
Hello,
I have code:
{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses, ScopedTypeVariables, TypeFamilies #-}
class C a b where c :: a -> b instance (int ~ Integer) => C Integer int where c = (+1)
c2 :: forall a b c. (C a b, C b c) => a -> c c2 x = c (c x :: b) c2 x = c ((c :: a -> b) x)
Why are the type signatures needed? If I leave all of them off, I get:
Could not deduce (C a1 a0) arising from the ambiguity check for ‛c2’ from the context (C a b, C a1 a) bound by the inferred type for ‛c2’: (C a b, C a1 a) => a1 -> b
from the line: c2 x = c (c x)
From my perspective, it seems that the type signature ghc infers should be able to restrict the ambiguous types as the hand-written signature does.
These concerns apply to HEAD (using -XAllowAmbiguousTypes) and ghc-7.6 too.
Regards, Adam _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users