A taste of programming in ML

Taking a new course Proglang which started this week. So expect more to follow on what I learn.

	(* returns NONE if list is empty, else SOME (maxnumber) *)
	fun max(numbers: int list) =
	if null numbers
	then NONE
	else
	let val max_tail = max(tl numbers)
	in
	if max_tail = NONE orelse hd numbers >= valOf max_tail
	then SOME (hd numbers)
	else max_tail
	end;
	(* concatenates all strings using separator *)
	fun stringjoin(strings: string list, separator: string) =
	if null strings
	then ""
	else if null (tl strings)
	then hd strings
	else hd strings ^ separator ^ stringjoin(tl strings, separator);
	(* date is tuple of form (year, month, day) -> returns boolean *)
	fun isLeapYear(date: int*int*int) =
	#1 date mod 400 = 0 orelse (#1 date mod 4 = 0 andalso #1 date mod 100 <> 0)
	(* filter all even numbers *)
	fun filterEven(numbers: int list) =
	if null numbers
	then []
	else if hd numbers mod 2 = 0
	then hd numbers :: filterEven(tl numbers)
	else filterEven(tl numbers);

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