59 lines
1.3 KiB
Text
59 lines
1.3 KiB
Text
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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### Contravariant Functors"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 21,
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"metadata": {},
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"outputs": [],
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"source": [
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"{-# LANGUAGE KindSignatures #-}\n",
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"\n",
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"-- (.) :: (b -> c) -> (a -> b) -> a -> c\n",
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"-- contraComp :: (a -> b) -> (b -> c) -> a -> c\n",
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"\n",
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"-- (.) f g x = f (g x)\n",
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"-- contraComp f g x = g (f x)\n",
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"\n",
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"-- instance Functor (a ->) where\n",
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"-- fmap = (.)\n",
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"\n",
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"-- instance Contravariant (-> z) where\n",
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"-- contramap = flip (.)\n",
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"\n",
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"newtype Predicate a = Predicate { getPredicate :: a -> Bool }\n",
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"\n",
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"newtype Op b a = Op { getOp :: a -> b }\n",
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" \n",
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"class Contravariant (f :: * -> *) where\n",
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" contramap :: (a -> b) -> f b -> f a\n",
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" \n",
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"instance Contravariant (Op a) where\n",
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" contramap f g = Op $ let bToa = getOp g in bToa . f"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Haskell",
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"language": "haskell",
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"name": "haskell"
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},
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"language_info": {
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"codemirror_mode": "ihaskell",
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"file_extension": ".hs",
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"name": "haskell",
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"pygments_lexer": "Haskell",
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"version": "8.8.3"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 4
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}
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