Failure to construct superclasses in instance
Consider
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, ConstraintKinds #-}
module Foo where
class Eq a => C a b
type X a = (Eq a, Show a)
instance X a => C a [b]HEAD gives
Foo.hs:8:10:
Could not deduce (Eq a)
arising from the superclasses of an instance declaration
from the context: X a
bound by the instance declaration at Foo.hs:8:10-23
Possible fix: add (Eq a) to the context of the instance declaration
In the instance declaration for ‘C a [b]’This is fall-out from refactoring the silent-superclass story. Patch coming.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.10.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |