PartialTypeSignatures suggests a redundant constraint with constraint families
When I say
{-# LANGUAGE ConstraintKinds, TypeFamilies #-}
module Bug where
type family ShowSyn a where ShowSyn a = Show a
foo :: (ShowSyn a, _) => a -> String
foo x = show x
I get
Bug.hs:7:20: error:
Found constraint wildcard ‘_’ standing for ‘Show a’
To use the inferred type, enable PartialTypeSignatures
In the type signature:
foo :: (ShowSyn a, _) => a -> String
But if I fill in my wildcard with Show a
, I'll rightly get a redundant constraint. Just a vanilla type synonym works there, but the type family causes trouble.
Trac metadata
Trac field | Value |
---|---|
Version | 8.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |