Hi,
I have stumbled across some strange behaviour in ghc7.
The following compiles fine with ghc 6.12.3:
{-# LANGUAGE ImplicitParams #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE NoMonomorphismRestriction #-}
module Test where
class C t where
type TF t
ttt :: TF t -> t
b :: (C t, ?x :: TF t) => t
b = ttt ?x
but ghc7 says:
Could not deduce (?x::TF t)
arising from a use of implicit parameter `?x'
from the context (C t, ?x::TF t)
bound by the type signature for b :: (C t, ?x::TF t) => t
at Test.hs:13:1-10
In the first argument of `ttt', namely `?x'
In the expression: ttt ?x
In an equation for `b': b = ttt ?x
Moreover, when I comment out the type declaration for b, it compiles and the
inferred type for b is identical to the one in the above program:
*Test> :t b
b :: (C t, ?x::TF t) => t
It feels to me like a bug but I am not entirely confident. Any ideas?
Michal
--
|o| Michal Konecny