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|
{-# LANGUAGE LinearTypes #-}
{-# LANGUAGE NoImplicitPrelude #-}
module Arity2 where
{-
inplace/bin/ghc-stage1 -O2 -dcore-lint
-}
--import GHC.Base
data Id a = Id a
(<$>) :: (a -> b) -> Id a -> Id b
(<$>) f (Id a) = Id (f a)
(<*>) :: Id (a -> b) -> Id a -> Id b
(<*>) (Id a) (Id b) = Id (a b)
data Q = Q () ()
data S = S ()
-- Q only gets eta-expand once and then trapped
foo = Q <$> Id () <*> Id ()
-- This compiles fine
foo2 = S <$> Id ()
{-
[1 of 1] Compiling Arity2 ( linear-tests/Arity2.hs, linear-tests/Arity2.o )
linear-tests/Arity2.hs:21:7: error:
• Couldn't match type ‘() ⊸ Q’ with ‘() -> b’
Expected type: Id (() -> b)
Actual type: Id (() ⊸ Q)
• In the first argument of ‘(<*>)’, namely ‘Q <$> Id ()’
In the expression: Q <$> Id () <*> Id ()
In an equation for ‘foo’: foo = Q <$> Id () <*> Id ()
• Relevant bindings include
foo :: Id b (bound at linear-tests/Arity2.hs:21:1)
|
21 | foo = Q <$> Id () <*> Id ()
| ^^^^^^^^^^^
-}
|
