signature Prelude=
sig 
   exception Error of string
   val error : string -> 'a
   val mkRandom : int -> int -> int
   val time : ('a -> 'b) -> 'a list -> ('b * int) list
end;

functor PRELUDE() =
struct
   exception Error of string;

   fun error s = raise Error s;

   local
   fun timeone f x =
      let val start  = System.processtime()
          val result = f x
          in
              (result, System.processtime() - start)
          end;
   in
   fun time f = map (timeone f);
   end;

  (* Given a seed, mkRandom returns a psuedo-random number generator
     which takes an integer argument of one more than the maximum
     return value required. ( Linear Congruential, after Sedgewick,
     "Algorithms", Addison-Wesley, 1983, Chapter 3 pp 37-38.) *)

  fun mkRandom seed = 
        let val r = ref seed
	    val a = 31415821
	    val m = 100000000

	    fun f n =
	      let val rand = (r := ((a * !r + 1) mod m);
			      (!r * n) div m)
	      in if n < 0 then rand + 1 else rand
	      end
         in f
        end;

fun max a b :int = if a > b then a else b
fun min a b :int = if a < b then a else b

exception Maxl
exception Minl
fun maxl []       = raise Maxl
  | maxl [a]      = a
  | maxl (h :: t) = max h (maxl t)

fun minl []       = raise Minl
  | minl [a]      = a
  | minl (h :: t) = min h (minl t)

fun sum []        = 0
  | sum (h :: t)  = h + sum t

fun prod []       = 1
  | prod (h :: t) = h * prod t

fun times a b = a * b : int
and plus  a b = a + b : int
and mult  a b = a * b : real
and add   a b = a + b : real

fun stringOfInt (i:int) = PolyML.makestring i;
end;