4.11 dies for certain RULES

Given

<code>
module Bug where

foo 1 = 2
bar 0 = 1

{-# RULES

  "foo/bar" foo bar = foobar

 #-}

foobar = 2
</code>

4.11 (couple of weeks old) dies with

  ghc-4.11: panic! (the `impossible' happened):
  	  basicTypes/Var.lhs:185: Non-exhaustive patterns in function readMutTyVar

4.08.1 doesn't seem to have a problem with this code.

Trac metadata

Trac field	Value
Version	None
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	ResolvedFixed
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
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Operating system
Architecture