Levity polymorphic GADT requires extra type signatures
This does not compile:
data Foo s (a :: TYPE k) where
FooC :: Foo s Int#
However, this does:
data Foo (s :: Type) (a :: TYPE k) where
FooC :: Foo s Int#
This also works:
data Foo (s :: j) (a :: TYPE k) where
FooC :: Foo s Int#
These are all of the language pragmas I have enabled:
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE TypeInType #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE UnboxedSums #-}
{-# LANGUAGE UnboxedTuples #-}
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-}
This is pretty easy to work around, but I think it's an incorrect behavior.
Trac metadata
Trac field | Value |
---|---|
Version | 8.2.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | low |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |