Celestin Apprentice 7/Apprentice-Release7.iso/Source Code/C/Applications/Moscow ML 1.42/src/test/test7.sml

Text File | 1997-08-18 | 398 b | 18 lines | [TEXT/R*ch]

abstype 'a Stack =
    EMPTY
  | PUSH of 'a StackTop
withtype 'a StackTop = 'a * 'a Stack
with
  exception EmptyStack;
  val empty = EMPTY;
  fun top EMPTY = raise EmptyStack
    | top (PUSH(x, _)) = x;
  fun push x stack = PUSH(x, stack);
  fun pop EMPTY = raise EmptyStack
    | pop (PUSH(_, rest)) = rest;
end;

val st1 = push 3 (push 2 (push 1 empty));
val top1 = top st1;
val rest1 = pop st1;