31 lines
No EOL
567 B
Standard ML
31 lines
No EOL
567 B
Standard ML
use "operators.sml";
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fun cons head tail = head :: tail
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fun fold f acc lst =
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case lst of
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[] => acc
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| head :: tail => fold f (f head acc) tail
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fun reverse lst =
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let
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fun f elm acc = elm :: acc
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in
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fold f [] lst
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end
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fun filter predicate lst =
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let
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fun f elm acc = if predicate elm then elm :: acc else acc
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in
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lst |> fold f [] |> reverse
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end
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fun empty lst = lst = []
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(* not efficient but works *)
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fun exists elem lst =
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lst
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|> filter (fn needle => elem = needle)
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|> empty
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|> not |