compiler exception when -> is used instead of => in instance definition

When running ghci on the attached file, the following exception is raised:

*** Exception: compiler/rename/RnSource.lhs:430:14-81: Irrefutable pattern failed for pattern Data.Maybe.Just (inst_tyvars,
                                                        _,
                                                        SrcLoc.L _ cls,
                                                        _)

It seems to stem from accidentally using -> instead of => in the following instance definition:

instance (ListConcat xs ys zs) -> ListConcat (x ::: xs) ys (x ::: zs)
  where listConcat = undefined

Trac metadata

Trac field	Value
Version	7.4.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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