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58 lines
1.6 KiB
58 lines
1.6 KiB
module Zipper exposing (..)
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type alias Zipper a =
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{ before : List a
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, focus : a
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, after : List a
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}
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{- Basic conversion -}
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fromList : a -> List a -> Zipper a
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fromList a l = Zipper [] a l
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toList : Zipper a -> List a
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toList rl = List.reverse rl.before ++ [rl.focus] ++ rl.after
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{- Functor like things -}
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map : (a -> b) -> Zipper a -> Zipper b
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map f rl = Zipper (List.map f rl.before) (f rl.focus) (List.map f rl.after)
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edit : (a -> a) -> Zipper a -> Zipper a
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edit f rl = Zipper rl.before (rl.focus |> f) rl.after
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{- Comonad functions -}
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extract : Zipper a -> a
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extract rl = rl.focus
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duplicate : Zipper a -> Zipper (Zipper a)
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duplicate rl = let
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lefts = iterate1N (List.length rl.before) shiftRight rl
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rights = iterate1N (List.length rl.after) shiftLeft rl
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in Zipper lefts rl rights
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extend : (Zipper a -> b) -> Zipper a -> Zipper b
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extend f w = map f (duplicate w)
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(=>>) : Zipper a -> (Zipper a -> b) -> Zipper b
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(=>>) = flip extend
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{- Domain functions -}
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shiftLeft : Zipper a -> Zipper a
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shiftLeft rl = case rl.after of
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[] -> case List.reverse rl.before of
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[] -> Zipper [] rl.focus []
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x::xs -> Zipper [rl.focus] x xs
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x::xs -> Zipper (rl.focus :: rl.before) x xs
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shiftRight : Zipper a -> Zipper a
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shiftRight rl = case rl.before of
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[] -> case List.reverse rl.after of
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[] -> Zipper [] rl.focus []
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x::xs -> Zipper xs x [rl.focus]
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x::xs -> Zipper xs x (rl.focus :: rl.after)
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{- From here we have private functions -}
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iterate1N : Int -> (a -> a) -> a -> List a
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iterate1N n f a = case n of
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0 -> []
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m -> f a :: List.map f (iterate1N (m - 1) f a)
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