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 |