#2494: Panic in tcSimplifyRuleLhs
------------------------+---------------------------------------------------
Reporter: rl | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.8.3 | Severity: normal
Keywords: | Testcase:
Architecture: Unknown | Os: Unknown
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With this module, both 6.8.3 and the HEAD panic in `tcSimplifyRuleLhs`:
{{{
{-# LANGUAGE Rank2Types, ScopedTypeVariables #-}
module Foo where
foo :: (forall m. Monad m => Maybe (m a) -> Maybe (m a)) -> Maybe a ->
Maybe a
foo _ x = x
{-# RULES
"foo/foo"
forall (f :: forall m. Monad m => Maybe (m a) -> Maybe (m a))
(g :: forall m. Monad m => Maybe (m b) -> Maybe (m b)) x.
foo f (foo g x) = foo (f . g) x
#-}
}}}
Note that the rule is incorrectly typed; with the correct types, no panic
happens.
Incidentially, I'm not sure if `ScopedTypeVariables` should be required
here.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2494>
GHC <http://www.haskell.org/ghc/>
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