Kind variables not allowed in class instance declarations
Consider the following code:
{-# LANGUAGE KindSignatures, PolyKinds, DataKinds, RankNTypes #-}
data KProxy (a :: *) = KP
class KindClass (kp :: KProxy k)
instance KindClass (KP :: KProxy [k])
The last line fails to compile, producing the following error message:
Not in scope: type variable `k'
However, there is a workaround. When I change the last line to
instance forall (a :: k). KindClass (KP :: KProxy [k])
all is good. Unfortunately, this last line requires the declaration of an unused type variable a
, which is a little messy.
This was tested on 7.5.20120426.
Trac metadata
Trac field | Value |
---|---|
Version | 7.5 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | #6064 (closed) |
Blocking | |
CC | |
Operating system | |
Architecture |