hw1/WashingtonPLMOOC

hw1.sml

fun is_older(date1 : int*int*int, date2: int*int*int) = 
    if #1 date1 <> #1 date2
    then 
	if #1 date1 < #1 date2
	then true
	else false
    else 
	if #2 date1 <> #2 date2
	then 
            if #2 date1 < #2 date2
	    then true
            else false
	else 
	    if #3 date1 < #3 date2
            then true
	    else false

fun number_in_month(dates : (int * int * int) list, month : int) = 
    if null dates
    then 0
    else  
	let 
	    val cnt = number_in_month(tl dates, month)
	in 
	    if #2 (hd dates) = month
            then cnt + 1
	    else cnt
        end

fun number_in_months(dates : (int * int * int) list, months : int list) = 
    if null months
    then 0
    else number_in_month(dates, hd months) + number_in_months(dates, tl months)

fun dates_in_month(dates : (int * int * int) list, month : int) =
    if null dates
    then []
    else
	let val l = dates_in_month(tl dates, month)
	in
	    if #2 (hd dates) = month
	    then (hd dates) :: l
	    else l
	end

fun dates_in_months(dates : (int * int * int) list, months : int list) = 
    if null months
    then []
    else dates_in_month(dates, hd months) @ dates_in_months(dates, tl months)

fun get_nth(strs : string list, n : int) = 
    if n = 1
    then hd strs
    else get_nth(tl strs, n - 1)

fun date_to_string(date : int * int * int) =
    let 
	val months = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]
    in
	get_nth(months, #2 date) ^ " " ^ Int.toString(#3 date) ^ ", " ^ Int.toString(#1 date)
    end
 

(*
//standard version
fun number_before_reaching_sum (sum : int, lst : int list) =
    if sum <= hd lst
    then 0
    else 1 + number_before_reaching_sum(sum - hd lst, tl lst)*)

fun number_before_reaching_sum(sum : int, posInts : int list) = 
    let
	fun aux(s : int, ints : int list, cnt : int) =
	    let
		val firstInt = hd ints
		val secondInt = hd (tl ints)
	    in	
		if cnt = 1 andalso s <= firstInt
		then 0
		else
		    if s > firstInt andalso s - firstInt > secondInt
		    then aux(s - firstInt, tl ints, cnt + 1)	
		    else cnt
	    end
    in 
	aux(sum, posInts, 1)
    end

fun what_month(day : int) =
    let
	val ints = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
    in
	number_before_reaching_sum(day, ints) + 1
    end
	
fun month_range(day1 : int, day2 : int) = 
    if day1 > day2
    then []
    else what_month(day1) :: month_range(day1 + 1, day2) 

fun oldest(dates : (int * int * int) list) = 
    if null dates
    then NONE
    else
	let
	    val old = oldest(tl dates)
	in 
	    if isSome(old) andalso is_older(valOf(old), hd dates)
	    then old
	    else SOME(hd dates)
	end