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 |
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| BlockedBy |
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| Related |
|
| Blocking |
|
| CC |
|
| Operating system |
|
| Architecture |
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