#5400: GHC loops on compiling with optimizations
-------------------------------+--------------------------------------------
Reporter: noschinl | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.0.4 | Keywords:
Testcase: | Blockedby:
Os: Linux | Blocking:
Architecture: x86_64 (amd64) | Failure: Compile-time crash
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When compiling the snippet below with optimizations enabled (i.e. `ghc -O
test.hs`), GHC does not seem to terminate. This happens with at least
7.0.3 and 7.0.4. Without optimizations, it builds fine.
{{{
data A = A Int
class C a where
fromHsk :: C a => a -> Int
instance C Int where
fromHsk = fromHsk
instance C A where
fromHsk (A s) = fromHsk s
main = undefined
}}}
When building this example with GHC 6.12.4, it fails with a complaint
about the bogus type constraints in the declaration of fromHsk:
{{{
test.hs:3:0:
All of the type variables in the constraint `C a'
are already in scope (at least one must be universally quantified
here)
(Use -XFlexibleContexts to lift this restriction)
When checking the class method: fromHsk :: (C a) => a -> Int
In the class declaration for `C'
}}}
After removing these unneeded constraint (i.e. changing the declaration of
`fromHsk` to `fromHsk :: a -> Int`, the snippet above builds even with GHC
7.0.4 and optimizations.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5400>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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