33 lines
745 B
Standard ML
33 lines
745 B
Standard ML
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(* year * month * day *)
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type Date = int * int * int
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fun fold f lst acc =
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case lst of
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[] => acc
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| head::tail => fold f tail (f head acc)
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fun is_older (
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(y1, m1, d1): Date,
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(y2, m2, d2): Date
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): bool =
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let
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val same_dates = y1 = y2 andalso m1 = m2 andalso d1 = d2
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val older = y1 <= y2 andalso m1 <= m2 andalso d1 <= d2
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in
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if same_dates then false else older
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end
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fun number_in_month (
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dates: Date list,
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month_to_find: int
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): int =
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let
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fun count_month (_, month, _) occurences =
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if month = month_to_find
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then occurences + 1
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else occurences
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in
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fold count_month dates 0
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end
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