type error causes type checker stack overflow

The following code causes

*** Exception: stack overflow

during type checking. I've tried to whittle the test case down, this may not be minimal. The (Ord a) instances and the unused vertexID member of the datatype seem to be necessary, otherwise the infinite type is correctly caught. Does not occur under 6.6.1

module GHCBug(
  MeshVertex(..)
  ) where

data (Ord a) => MeshVertex a b = MeshVertex {
  vertexID         :: a,
  vertexChildren   :: [a]
  } deriving (Show)

split :: (Ord a)   =>
  a                ->
  [MeshVertex a b] ->
  [MeshVertex a b]
split a m = let
    av      = head m
    newVTs  = preSplit a m
    av'     = av { vertexChildren = newVTs }
    newMVs  = av' : m
    newMesh = newMVs
  in newMesh

preSplit :: (Ord a) =>
  a                 ->
  [MeshVertex a b]  ->
  [MeshVertex a b]
preSplit a m = preSplit a $ split a m

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	MacOS X
Architecture	x86