currying.sml

(* old way to get the effect of multiple arguments *)
fun sorted3_tupled (x,y,z) = z >= y andalso y >= x

val t1 = sorted3_tupled (7,9,11)

(* new way: currying *)

val sorted3 = fn x => fn y => fn z => z >= y andalso y >= x

(*fun sorted3 x = fn y fn z => ... *)

val t2 = ((sorted3 7) 9) 11

val t3 = sorted3 7 9 11

(*
val wrong1 = sorted2_tupled 7 9 11
val wrong2 = sorted3 (7,9,11)
*)

fun sorted3_nicer x y z = z >= y andalso y >= x

val t4 = sorted3_nicer 7 9 11
val t5 = ((sorted3_nicer 7) 9) 11


(* a more useful example *)
fun  fold f acc xs = (* means fun fold f = fn acc => fn xs => *)
     case xs of
	 [] => acc
      | x::xs'  => fold f (f(acc,x)) xs'

(* a call to curried fold: will improve this call next *)
fun sum xs = fold (fn (x,y) => x+y) 0 xs