blob: 0852468233bd289851c0a64da43c84e5638e61e2 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
|
{-# LANGUAGE PartialTypeSignatures #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# OPTIONS_GHC -fno-warn-partial-type-signatures #-}
type Empty a = ()
foo :: expr a -> expr a -> expr (Empty a)
foo = undefined
newtype Expr a = SPT {run :: String}
pt1 :: forall a ptexpr . ptexpr a -> ptexpr (Empty a)
pt1 a = foo a a
pt2 :: forall a ptexpr . ptexpr a -> ptexpr _
pt2 a = foo a a
main :: IO ()
main = do
-- This typechecks without any trouble.
putStrLn $ run $ pt1 @Int @Expr undefined
-- This should also typecheck, but doesn't since GHC seems to mix up the
-- order of the type variables.
putStrLn $ run $ pt2 @Int @Expr undefined
|
