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59 lines
865 B
Text
59 lines
865 B
Text
module ListOps exposing (..)
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length : List a -> Int
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length list =
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foldl (\_ acc -> 1 + acc) 0 list
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reverse : List a -> List a
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reverse list =
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foldl (::) [] list
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foldl : (a -> b -> b) -> b -> List a -> b
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foldl f acc list =
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case list of
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[] ->
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acc
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head :: tail ->
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foldl f (f head acc) tail
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foldr : (a -> b -> b) -> b -> List a -> b
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foldr f acc list =
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case list of
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[] ->
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acc
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head :: tail ->
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f head (foldr f acc tail)
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map : (a -> b) -> List a -> List b
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map f list =
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foldr (\x acc -> f x :: acc) [] list
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filter : (a -> Bool) -> List a -> List a
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filter f list =
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foldr
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(\x acc ->
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if f x then
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x :: acc
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else
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acc
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)
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[]
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list
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append : List a -> List a -> List a
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append xs ys =
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foldr (::) ys xs
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concat : List (List a) -> List a
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concat list =
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foldr append [] list
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