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2 changed files with 276 additions and 11 deletions
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@ -1,17 +1,41 @@
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(* year * month * day *)
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type Date = int * int * int
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(*
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Pipe operator.
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Simply to write code like "data |> fun" instead "fun data".
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Then you can "pipe" results to functions via partial application:
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fun square a b = a * b
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fun sum a b = a + b
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10 |> sum 10 |> square 2 // 40
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*)
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fun |> (x, f) = f x
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infix |>
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(* composition operator *)
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fun $ (f, x) = f x
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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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infix |>
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infix $
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fun fold f acc lst =
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if lst = []
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then acc
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else
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let
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val tail = tl lst
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val head = hd lst
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in
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fold f (f head acc) tail
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end
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fun reverse lst =
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fold (fn elm => fn acc => elm :: acc) 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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(* non tail optimized :( *)
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@ -25,18 +49,39 @@ fun reverse lst =
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fun filter predicate lst =
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let
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val reversed = reverse lst
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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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fold f reversed []
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lst |> fold f [] |> reverse
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end
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fun range from to =
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let
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fun generate from to acc =
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if from > to
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then acc
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else generate (from + 1) to (from :: acc)
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in
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generate from to [] |> reverse
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end
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(* naive sort, will blow up stack :( *)
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fun sort f lst =
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case lst of
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[] => []
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| hd :: [] => [hd]
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| first :: second :: rest =>
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if f first second
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then second :: first :: sort f rest
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else first :: second :: sort f rest
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fun is_older ((y1, m1, d1): Date, (y2, m2, d2): Date): 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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if same_dates
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then false
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else older
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end
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fun number_in_month (dates: Date list, month_to_find: int): int =
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@ -46,7 +91,7 @@ fun number_in_month (dates: Date list, month_to_find: int): int =
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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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fold count_month 0 dates
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end
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fun number_in_months (dates: Date list, months_to_find: int list): int =
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@ -54,7 +99,7 @@ fun number_in_months (dates: Date list, months_to_find: int list): int =
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fun count_months month acc =
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acc + number_in_month (dates, month)
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in
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fold count_months months_to_find 0
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fold count_months 0 months_to_find
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end
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fun dates_in_month (dates: Date list, in_month: int): Date list =
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@ -62,4 +107,88 @@ fun dates_in_month (dates: Date list, in_month: int): Date list =
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fun filter_dates (_, month, _) = in_month = month
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in
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filter filter_dates dates
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end
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fun dates_in_months (dates: Date list, in_months: int list): Date list =
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let
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fun filter_dates month filtered =
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filtered @ dates_in_month (dates, month)
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in
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fold filter_dates [] in_months
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end
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fun get_nth (strings: string list, nth: int): string =
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let
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fun find str (pos, found) =
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if pos = nth
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then (pos + 1, str)
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else (pos + 1, found)
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in
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fold find (1, "") strings |> #2
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end
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(* this function will create list for months on every call :( *)
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fun date_to_string ((year, month, day): Date): string =
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let
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val months = [
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"January",
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"February",
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"March",
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"April",
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"May",
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"June",
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"July",
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"August",
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"September",
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"October",
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"November",
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"December"
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]
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val string_month = get_nth (months, month - 1)
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val to_str = Int.toString
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fun pad num =
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if num < 10
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then "0" ^ to_str num
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else to_str num
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in
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string_month ^ " " ^ pad day ^ ", " ^ to_str year
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end
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fun number_before_reaching_sum (sum: int, numbers: int list): int =
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if numbers = [] orelse hd numbers >= sum
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then 0
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else 1 + number_before_reaching_sum ((sum - hd numbers), tl numbers)
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fun what_month (day: int): int =
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let
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val months = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
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in
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number_before_reaching_sum (day, months) + 1
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end
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(* correct but to complex for such problem *)
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(* fun month_range (day1: int, day2: int): int list =
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let
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fun append_month day months = what_month day :: months
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in
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range day1 day2 |> fold append_month [] |> reverse
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end
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*)
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fun month_range (day1: int, day2: int): int list =
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if day1 > day2
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then []
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else what_month day1 :: month_range (day1 + 1, day2)
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fun oldest (dates: Date list): Date option =
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let
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fun compare a b = not $ is_older (a, b)
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in
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if dates = []
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then NONE
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else sort compare dates |> hd |> SOME
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end
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@ -1,6 +1,19 @@
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use "test.sml";
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use "date.sml";
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val () =
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assert
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(range 1 2 = [1, 2])
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"range: generates sequence in right order"
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val () = assert (sort (fn a => fn b => a > b) [] = []) "sort: empty list"
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val () = assert (sort (fn a => fn b => a > b) [1] = [1]) "sort: one val"
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val () =
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assert
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(sort (fn a => fn b => a > b) [2, 1] = [1, 2])
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"sort: two elements"
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val () =
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assert
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(is_older ((1999, 12, 31), (1999, 12, 31)) = false)
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@ -119,4 +132,127 @@ val () =
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"dates_in_month: filter non matching dates"
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end
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val () =
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let
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val dates = []
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val months = []
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val expect = []
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in
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assert
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(dates_in_months (dates, months) = expect)
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"dates_in_months: empty lists"
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end
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val () =
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let
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val dates = [(2000, 11, 31), (2000, 12, 30), (2000, 12, 31)]
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val months = [11]
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val expect = [(2000, 11, 31)]
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in
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assert
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(dates_in_months (dates, months) = expect)
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"dates_in_months: match one date with one month"
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end
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val () =
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let
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val dates = [(2000, 11, 31), (2000, 12, 30), (2000, 12, 31)]
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val months = [11, 12]
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val expect = dates
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in
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assert
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(dates_in_months (dates, months) = expect)
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"dates_in_months: match three dates with 2 months"
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end
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val () =
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assert
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(get_nth (["first"], 1) = "first")
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"get_nth: get first element"
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val () =
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assert
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(get_nth (["first", "second", "third"], 3) = "third")
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"get_nth: get third element"
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val () =
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assert
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(get_nth (["first", "second", "third"], 4) = "")
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"get_nth: not found index returns empty string :)"
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val () =
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assert
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(date_to_string ((2020, 06, 01)) = "May 01, 2020")
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"date_to_string: returns correct string"
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val () =
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assert
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(number_before_reaching_sum (12, []) = 0)
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"number_before_reaching_sum: empty list returns zero"
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val () =
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assert
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(number_before_reaching_sum (12, [1]) = 1)
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"number_before_reaching_sum: one list element"
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val () =
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assert
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(number_before_reaching_sum (12, [4, 5, 1, 3]) = 3)
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"number_before_reaching_sum: list with overflowing sum"
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val () =
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assert
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(number_before_reaching_sum (12, [12, 2]) = 0)
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("number_before_reaching_sum:" ^
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"first element already equals to sum but there is more")
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val () =
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assert (what_month 365 = 12) "what_month: last day of a year"
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val () =
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let
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val day1 = 1
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val day2 = 2
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val expect = [1, 1]
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in
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assert
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(month_range (day1, day2) = expect)
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"what_month: frist 2 days of a year"
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end
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val () =
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let
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val day1 = 31
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val day2 = 33
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val expect = [1, 2, 2]
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in
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assert
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(month_range (day1, day2) = expect)
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"what_month: three days in two different months"
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end
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val () =
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let
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val dates = []
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val expect = NONE
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in
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assert (oldest dates = expect) "oldest: retruns NONE on empty list"
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end
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val () =
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let
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val dates = [(2000, 11, 31)]
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val expect = SOME (2000, 11, 31)
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in
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assert (oldest dates = expect) "oldest: retruns SOME date"
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end
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val () =
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let
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val dates = [(2020, 11, 31), (2021, 11, 31)]
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val expect = SOME (2020, 11, 31)
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in
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assert (oldest dates = expect) "oldest: retruns oldest"
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end
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val () = complete ()
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