class C a b | a -> b; (C a b, Eq b) => a -- not legal
The following fragment is not accepted:
class C a b | a -> b where f :: a -> b
g :: (C a b, Eq b) => a -> Bool
g x = f x == f x
Ambiguous type variable(s) `b' in the constraint `Eq b'
arising from use of `==' at Test.hs:4
In the right-hand side of an equation for `g': (f x) == (f x)
Hugs accepts it.
Trac metadata
| Trac field | Value |
|---|---|
| Version | None |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | ResolvedFixed |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |
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