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{-# LANGUAGE LinearTypes #-}
{-# LANGUAGE NoImplicitPrelude #-}
module Op where
{-
See Control.Arrow and Data.Functor.Contravariant
-}
import GHC.Base
class Or p where
or :: p a b -> p a b -> p a b
instance Or (->) where
or x _ = x
foo = or Just (\x -> Just x)
{-
This caused an error in the earlier version of linear types:
linear-tests/Op.hs:18:16: error:
• Couldn't match expected type ‘a ⊸ Maybe a’
with actual type ‘a0 -> Maybe a0’
• The lambda expression ‘\ x -> Just x’ has one argument,
its type is ‘p0 a b0’,
it is specialized to ‘a ⊸ Maybe a’
In the second argument of ‘or’, namely ‘(\ x -> Just x)’
In the expression: or Just (\ x -> Just x)
• Relevant bindings include
foo :: a ⊸ Maybe a (bound at linear-tests/Op.hs:18:1)
|
18 | foo = or Just (\x -> Just x)
| ^^^^^^^^^^^^
-}
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