Wrong inferred type shown

When the warning for missing type signatures is turned on the displayed type is sometimes totally bogus.

{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, UndecidableInstances #-}
module Bug where

class C a b | a -> b, b -> a where
    f :: a -> b

instance C Int Bool where
    f = undefined
instance (C a c, C b d) => C (a -> b) (c -> d) where
    f = undefined

foo :: Int -> Int
foo = undefined

bar = f foo

GHC says:

    Warning: Definition but no type signature for `bar'
             Inferred type: bar :: c -> d

The type for bar is, of course, Bool->Bool, and nothing else.

-- Lennart

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	lennart@augustsson.net
Operating system
Architecture