type family does not get expanded in ghc-6.12.1
The following code (which is a trimmed down version of an application of the multirec library) does not compile on ghc-6.12.1, but it does with ghc-6.10.4. Why?
{-# LANGUAGE GADTs, TypeFamilies #-}
type family TF a :: * -> *
type instance TF () = App (Equ ())
data Equ ix ix' where Refl :: Equ ix ix
data App f x = App (f x)
-- does not typecheck in 6.12.1 (but works in 6.10.4)
bar :: TF () () -> ()
bar (App Refl) = ()
-- does typecheck in 6.12.1 and 6.10.4
ar :: App (Equ ()) () -> ()
ar (App Refl) = ()
Trac metadata
Trac field | Value |
---|---|
Version | 6.12.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | andres@cs.uu.nl, jpm@cs.uu.nl, stefan@cs.uu.nl |
Operating system | |
Architecture |