PROGRAM 4


(*  filename:  prog9.sml     author:  anthony f. ortiz  *)
(*  this program converts a list to a stack and a stack to a list.  *)
 
datatype 'a stack = empty | push of ('a * 'a stack);
 
fun list_to_stack (l: 'a list): 'a stack =
    if null (l) then
        empty
    else
        push (hd (l), list_to_stack (tl (l)));
 
fun stack_to_list (empty) = nil
| stack_to_list (push (x, y)) = [x] @ stack_to_list (y);
 
list_to_stack ([]);
list_to_stack ([1]);
list_to_stack ([1, 2]);
list_to_stack ([1, 2, 3]);
 
stack_to_list (empty);
stack_to_list (push (1, empty));
stack_to_list (push (1, push (2, empty)));
stack_to_list (push (1, push (2, push (3, empty))));
 
list_to_stack ([]);
list_to_stack (["cat"]);
list_to_stack (["cat", "dog"]);
list_to_stack (["cat", "dog", "rat"]);
 
stack_to_list (empty);
stack_to_list (push ("cat", empty));
stack_to_list (push ("cat", push ("dog", empty)));
stack_to_list (push ("cat", push ("dog", push ("rat", empty))));

(*  filename:  prog9.out     author:  anthony f. ortiz  *)
 
Standard ML of New Jersey, Version 110.0.6, October 31, 1999 [CM; autoload enabl
ed]
- use "prog9.sml";
[opening prog9.sml]
datatype 'a stack = empty | push of 'a * 'a stack
val list_to_stack = fn : 'a list -> 'a stack
GC #0.0.0.0.1.7:   (0 ms)
val stack_to_list = fn : 'a stack -> 'a list
prog9.sml:15.1-15.19 Warning: type vars not generalized because of
   value restriction are instantiated to dummy types (X1,X2,...)
val it = empty : ?.X1 stack
val it = push (1,empty) : int stack
val it = push (1,push (2,empty)) : int stack
val it = push (1,push (2,push #)) : int stack
prog9.sml:20.1-20.22 Warning: type vars not generalized because of
   value restriction are instantiated to dummy types (X1,X2,...)
val it = [] : ?.X1 list
val it = [1] : int list
val it = [1,2] : int list
val it = [1,2,3] : int list
prog9.sml:25.1-25.19 Warning: type vars not generalized because of
   value restriction are instantiated to dummy types (X1,X2,...)
val it = empty : ?.X1 stack
val it = push ("cat",empty) : string stack
val it = push ("cat",push ("dog",empty)) : string stack
val it = push ("cat",push ("dog",push #)) : string stack
prog9.sml:30.1-30.22 Warning: type vars not generalized because of
   value restriction are instantiated to dummy types (X1,X2,...)
val it = [] : ?.X1 list
val it = ["cat"] : string list
val it = ["cat","dog"] : string list
val it = ["cat","dog","rat"] : string list
val it = () : unit
- ^Z
Stopped (user)




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