Typechecker loop with type families
The following code (which I think is ill-typed) causes GHC to hang, both on 6.12.1 and 6.13.20100616:
{-# LANGUAGE TypeFamilies, ScopedTypeVariables, FlexibleContexts #-}
module Crash where
class Family f where
terms :: f a -> a
class Family (TermFamily a) => TermLike a where
type TermFamily a :: * -> *
laws :: forall a b. TermLike a => TermFamily a a -> b
laws t = prune t (terms (undefined :: TermFamily a a))
prune :: TermLike a => TermFamily a a -> TermFamily a a -> b
prune = undefinedThe compiler still hangs if I remove the typeclass constraints (everything to the left of a =>, I mean), but everything else seems to be necessary for the compiler to loop. Using -dshow-passes shows that it's the typechecker that loops.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 6.13 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |