#1795: typechecker loops on simple program with fundep
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Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.8
Severity: major | Keywords:
Difficulty: Unknown | Os: Multiple
Testcase: yes | Architecture: x86
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The program below causes the "Renamer/typechecker" phase to loop.
Confirmed with GHC 6.8.20070927 on Linux and 6.9.20071018 on Windows (so
I'm not absolutely certain it's present in latest 6.8, but it seems very
likely).
The program has an infinite type - the definition of translate causes
(String, a) to be unified with a. Removing the fundep in MkA causes a
reasonable error to be reported.
{{{
{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies,
FlexibleInstances #-}
module X() where
data A a = A
class MkA a b | a -> b where
mkA :: a -> A b
instance MkA a a where
translate :: (String, a) -> A a
translate a = mkA a
}}}
Ganesh
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1795>
GHC <http://www.haskell.org/ghc/>
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