Can't apply higher-ranked kind in type family
This code doesn't typecheck due to F2:
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeInType #-}
module Bug where
import Data.Kind
f :: (forall (a :: Type). a -> a) -> Bool
f g = g True
type F1 (g :: forall (a :: Type). a -> a) = g True
type family F2 (g :: forall (a :: Type). a -> a) :: Bool where
F2 g = g True$ /opt/ghc/8.2.1/bin/ghci Bug.hs
GHCi, version 8.2.0.20170623: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 1] Compiling Bug ( Bug.hs, interpreted )
Bug.hs:14:6: error:
• Expected kind ‘forall a. a -> a’, but ‘g’ has kind ‘Bool -> Bool’
• In the first argument of ‘F2’, namely ‘g’
In the type family declaration for ‘F2’
|
14 | F2 g = g True
| ^This is surprising to me, since F2 seems like the type family counterpart to f and F1, both of which typecheck.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.0.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |