list_infix_op.sml

fun op ** (a, b) = let
  val succ = fn x => x + 1
  val pred = fn x => x - 1
  val c = if a < b then succ a else pred a
in
  if a = b then [a] else a::(op ** (c ,b))
end;
infix **;

fun op *** (a, b) = let
  val succ = fn x => x + 1
  val pred = fn x => x - 1
  val c = if a < b then succ a else pred a
in
  if a = b then [] else a::(op *** (c, b))
end;
infix ***;

1 **  10;
(* val it = [1,2,3,4,5,6,7,8,9,10] : int list *)

1 *** 10;
(* val it = [1,2,3,4,5,6,7,8,9] : int list *)

3 ** ~3;
(* val it = [3,2,1,0,~1,~2,~3] : int list *)

~3 *** ~10;
(* val it = [~3,~4,~5,~6,~7,~8,~9] : int list *)