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7得票1回答
无法从f x = f₁ y推断出f = f₁吗？
{-# LANGUAGE GADTs #-} data Foo x y where Composition :: Foo b c -> Foo a b -> Foo a c FMap :: Functor f => (a->b) -> Foo (f a)...
{-# LANGUAGE GADTs #-} data Foo x y where Composition :: Foo b c -> Foo a b -> Foo a c FMap :: Functor f => (a->b) -> Foo (f a)...