#6041: Program hangs when run under Ubuntu Precise
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Reporter: dsf | Owner:
Type: bug | Status: new
Priority: high | Milestone: 7.4.2
Component: Compiler | Version: 7.4.1
Resolution: | Keywords:
Os: Linux | Architecture: Unknown/Multiple
Failure: Runtime crash | Difficulty: Unknown
Testcase: | Blockedby:
Blocking: | Related:
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Changes (by guest):
* status: closed => new
* resolution: worksforme =>
Comment:
Hello
I was very intrigued by this report, and hunted the bug for a long time,
but it's very simple. It's not GHC.
You did not define `state` for `Wrapper`. That's not bad, since the
documentation in mtl-2.1 states that minimal definition is `get`/`put`.
The default definition for `state` is:
{{{
state f = do
s <- get
let ~(a, s) = f s
put s
return a
}}}
but in transformers-0.3 you can find:
{{{
instance (Monad m) => Monad (StateT s m) where
return a = state $ \s -> (a, s)
[...]
}}}
so `state` and `return` are mutually calling themselves, and `state` in
second code should be `StateT`. Bug in transformers. I reopened the ticket
as I am unsure where to report this...
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:12>
GHC <http://www.haskell.org/ghc/>
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