#1241: Functional dependency Coverage Condition is lifted, and should not be
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Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 6.8
Component: Compiler (Type checker) | Version: 6.6
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Comment (by simonpj):
Stefan adds: Editing `Control.Monad.State.Strict` to remove `-fallow-
undecidable-instances`:
{{{
[EMAIL PROTECTED]:/tmp$ ghc -fglasgow-exts Control/Monad/State/Strict.hs
Control/Monad/State/Strict.hs:207:0:
Illegal instance declaration for `MonadError e (StateT s m)'
(the Coverage Condition fails for one of the functional
dependencies;
Use -fallow-undecidable-instances to permit this)
In the instance declaration for `MonadError e (StateT s m)'
Control/Monad/State/Strict.hs:213:0:
Illegal instance declaration for `MonadReader r (StateT s m)'
(the Coverage Condition fails for one of the functional
dependencies;
Use -fallow-undecidable-instances to permit this)
In the instance declaration for `MonadReader r (StateT s m)'
Control/Monad/State/Strict.hs:218:0:
Illegal instance declaration for `MonadWriter w (StateT s m)'
(the Coverage Condition fails for one of the functional
dependencies;
Use -fallow-undecidable-instances to permit this)
In the instance declaration for `MonadWriter w (StateT s m)'
}}}
Yes, these are the same instances that break h98 compatibility.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1241>
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