#2544: Improve "Can't unify" error messages from type functions
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Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: low | Milestone: 7.0.2
Component: Compiler (Type checker) | Version: 6.8.3
Keywords: | Testcase:
Blockedby: | Difficulty: Unknown
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Changes (by jwlato):
* cc: jwl...@… (added)
* failure: => None/Unknown
Comment:
With ghc-7.0.1, the error message is now:
{{{
bug.hs:11:12:
Could not deduce (IxMap r ~ IxMap i1) from the context (Ix l, Ix r)
NB: `IxMap' is a type function, and may not be injective
Expected type: IxMap (l :|: r) [Int]
Actual type: BiApp (IxMap l) (IxMap i1) [Int]
In the expression: BiApp empty empty
In an equation for `empty': empty = BiApp empty empty
In the instance declaration for `Ix (l :|: r)'
bug.hs:11:18:
Could not deduce (IxMap i ~ IxMap l) from the context (Ix l, Ix r)
NB: `IxMap' is a type function, and may not be injective
Expected type: IxMap l [Int]
Actual type: IxMap i [Int]
In the first argument of `BiApp', namely `empty'
In the expression: BiApp empty empty
In an equation for `empty': empty = BiApp empty empty
Failed, modules loaded: none.
}}}
Can this be closed? These error messages are much more useful (at least to
my eye).
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2544#comment:6>
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