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cqfd/Mappers.idr

Created September 19, 2021 04:56
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Mappers.idr
module Mappers
data Identity a = MkIdentity a
Functor Identity where
map f (MkIdentity x) = MkIdentity (f x)
repapply : Nat -> (a -> a) -> (a -> a)
repapply Z f = id
repapply (S k) f = f . repapply k f
mapND : Functor f => (n: Nat) -> (a -> b) -> (repapply n f $ a) -> (repapply n f $ b)
mapND 0 g x = g x
mapND 1 g x = map g x
mapND (S k) g x = (map . mapND k) g x
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cqfd commented Sep 19, 2021 •
edited
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Ok! Maybe this is a nicer/smaller version:

module Mappers

repapply : Nat -> (a -> a) -> (a -> a)
repapply Z f = id
repapply (S k) f = f . repapply k f

mapND : Functor f => (n: Nat) -> (a -> b) -> (repapply n f $ a) -> (repapply n f $ b)
mapND 0 g = g
mapND (S k) g = (map . mapND k) g

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