id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
1430,getC: Type signature needed when existential types are used but not in the type signature,igloo,,"This module:
{{{
{-# OPTIONS -fglasgow-exts #-}
module Q where

import Data.Typeable

data ExTypeable = forall a. Typeable a => ExTypeable a

-- unExTypeable :: Typeable h => ExTypeable -> Maybe h
unExTypeable (ExTypeable a) = cast a
}}}
with the type signature commented out gives this in the HEAD:
{{{
q.hs:10:30:
    Could not deduce (Typeable b) from the context (Typeable a)
      arising from a use of `cast' at q.hs:10:30-35
    Possible fix:
      add (Typeable b) to the context of the constructor `ExTypeable'
    In the expression: cast a
    In the definition of `unExTypeable':
        unExTypeable (ExTypeable a) = cast a
}}}
It works in 6.6.

It's part of the getC test.",bug,closed,high,6.8.1,Compiler (Type checker),6.6.1,fixed,,,Unknown/Multiple,Unknown/Multiple,,Unknown,"getC, tc228",,,