Type checker hangs

The following module causes ghc --make and ghci to hang. -ddump-tc-trace produces output indefinitely.

{-# LANGUAGE GADTs #-}
{-# LANGUAGE FlexibleContexts #-}

import Generics.MultiRec
import Control.Monad.Writer

data AnyF s f where
  AnyF :: s ix -> f ix -> AnyF s f

children :: HFunctor s (PF s) => s ix -> (PF s) r ix -> [AnyF s r]
children p x = execWriter (hmapM p collect x) where
  collect :: (HFunctor s (PF s)) => s ix -> r ix -> Writer [AnyF s r] (r ix)
  collect w x = tell [AnyF w x] >> return x

Module Generics.MultiRec is from Hackage package multirec-0.4.

The code contains a type error: if arguments p and collect are swapped the code compiles fine.

I haven't tried making this example any smaller.

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown/Multiple
Architecture	Unknown/Multiple