(* utilities *)

fun map f nil = nil
  | map f (h::t) = (f h)::(map f t);

fun fold f id nil = id
  | fold f id (h::t) = f h (fold f id t);

fun filter f nil = nil
  | filter f (h::t) = if (f h) then (h::(filter f t)) else (filter f t);

fun delete x L = filter (fn y => not(x = y)) L;

fun remdups nil = nil
  | remdups (h::t) = h::(remdups (delete h t));

fun member x nil = false
  | member x (h::t) = (x = h) orelse (member x t);

fun subset a b = fold (fn x => fn y => x andalso y) true 
			(map (fn x => member x b) a);

fun seteq a b = (subset a b) andalso (subset b a);

(* find nth element of a set, first = 1st *)
fun nth 1 (h::t) = h
  | nth n (h::t) = nth (n-1) t;

(* replaces nth element of list with x *)
fun replace x n nil = nil
  | replace x 1 (h::t) = (x::t)
  | replace x n (h::t) = h::(replace x (n-1) t);

fun list x = [x];

(* flattens a list of lists *)
fun flat l = fold (fn x => (fn y => x@y)) nil l;


(*    Painless I/O - what professors would do for students!   *)

(* call getstring with "getstring()"  *)
fun getstring () = TextIO.inputLine(TextIO.stdIn);
fun getint () = 
  let val (SOME x) = Int.fromString (TextIO.inputLine(TextIO.stdIn))
	in x end;
fun printint n = print (Int.toString(n));


(*  BASIC STRING OPERATIONS:

   "aa"^"bb" -> "aabb"
   Int.toString(4) -> "4"
*)