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https://github.com/idris-lang/Idris2.git
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dab2b0d146
If `(~>)` isn't publicly exported, the type checker doesn't know that `Mor` constructs something of type `~>`.
92 lines
2.0 KiB
Idris
92 lines
2.0 KiB
Idris
module Data.Morphisms
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public export
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record Morphism a b where
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constructor Mor
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applyMor : a -> b
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infixr 1 ~>
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public export
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(~>) : Type -> Type -> Type
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(~>) = Morphism
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public export
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record Endomorphism a where
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constructor Endo
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applyEndo : a -> a
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public export
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record Kleislimorphism (f : Type -> Type) a b where
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constructor Kleisli
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applyKleisli : a -> f b
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export
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Functor (Morphism r) where
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map f (Mor a) = Mor $ f . a
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export
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Applicative (Morphism r) where
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pure a = Mor $ const a
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(Mor f) <*> (Mor a) = Mor $ \r => f r $ a r
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export
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Monad (Morphism r) where
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(Mor h) >>= f = Mor $ \r => applyMor (f $ h r) r
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export
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Semigroup a => Semigroup (Morphism r a) where
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f <+> g = Mor $ \r => (applyMor f) r <+> (applyMor g) r
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export
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Monoid a => Monoid (Morphism r a) where
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neutral = Mor \r => neutral
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export
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Semigroup (Endomorphism a) where
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(Endo f) <+> (Endo g) = Endo $ g . f
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export
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Monoid (Endomorphism a) where
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neutral = Endo id
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export
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Functor f => Functor (Kleislimorphism f a) where
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map f (Kleisli g) = Kleisli (map f . g)
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export
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Applicative f => Applicative (Kleislimorphism f a) where
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pure a = Kleisli $ const $ pure a
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(Kleisli f) <*> (Kleisli a) = Kleisli $ \r => f r <*> a r
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export
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Monad f => Monad (Kleislimorphism f a) where
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(Kleisli f) >>= g = Kleisli $ \r => do
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k1 <- f r
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applyKleisli (g k1) r
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-- Applicative is a bit too strong, but there is no suitable superclass
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export
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(Semigroup a, Applicative f) => Semigroup (Kleislimorphism f r a) where
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f <+> g = Kleisli \r => (<+>) <$> (applyKleisli f) r <*> (applyKleisli g) r
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export
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(Monoid a, Applicative f) => Monoid (Kleislimorphism f r a) where
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neutral = Kleisli \r => pure neutral
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export
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Cast (Endomorphism a) (Morphism a a) where
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cast (Endo f) = Mor f
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export
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Cast (Morphism a a) (Endomorphism a) where
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cast (Mor f) = Endo f
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export
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Cast (Morphism a (f b)) (Kleislimorphism f a b) where
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cast (Mor f) = Kleisli f
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export
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Cast (Kleislimorphism f a b) (Morphism a (f b)) where
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cast (Kleisli f) = Mor f
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