Script started on Wed Nov 13 16:26:40 1991
warning: could not update utmp entry
simpson-04% sml
Standard ML of New Jersey, Version 0.66, 15 September 1990
val it = () : unit
- val p = ref 5 and q = ref 2;
val p = ref 5 : int ref
val q = ref 2 : int ref
- !p;
val it = 5 : int
- !q;
val it = 2 : int
- x = (p,q);
val x = (ref 5,ref 2) : int ref * int ref
- p := 99;
val it = () : unit
- !p;
val it = 99 : int
- x;
val it = (ref 99,ref 2) : int ref * int ref
- (p := !p + 1; q := !q + 1);
val it = () : unit
- x;
val it = (ref 100,ref 3) : int ref * int ref
- val l = [p,q];
val l = [ref 100,ref 3] : int ref list
- q:= 1234;
val it = () : unit
- x;
val it = (ref 100,ref 1234) : int ref * int ref
- l;
val it = [ref 100,ref 1234] : int ref list
- hd l;
val it = ref 100 : int ref
- !(hd l);
val it = 100 : int
- p = q;
val it = false : bool
- val pp = p;
val pp = ref 100 : int ref
- pp = p;
val it = true : bool
- q := 100;
val it = () : unit
- p = q;
val it = false : bool
- !p = !q;
val it = true : bool
- (* That is p does not equal q. They are different 
= however, they when dereference they are the same *)



- (* cyclic data structures ??? *)
- val f' = ref(fn k => k+1);
val f' = ref fn : (int -> int) ref
- !f' 3;
val it = 4 : int
- fun f n = if n = 0 then 1 else n * !f'(n-1);
val f = fn : int -> int
- f 3;
val it = 9 : int
- f 1;
val it = 1 : int
- f 2;
val it = 4 : int
- (* looks like f x = x*x *)
- f' := f;
val it = () : unit
- (* CLOSE THE KNOT *)
- f 1;
val it = 1 : int
- f 2;
val it = 2 : int
- f 3;
val it = 6 : int
- f 4;
val it = 24 : int
- (* f x is now x! *)


- (* vectors ???? *)
- use "vectors";
[opening vectors]
[closing vectors]
val it = () : unit
- val x = make_vector 5 (ref 0);
val x = Node (Node (Node #,ref #,Lf),ref 0,Node 
        (Node #,ref #,Lf)) : int ref tree
- (get x 1) := 1;
val it = () : unit
- get x 1;
val it = ref 1 : int ref
- get x 2;
val it = ref 1 : int ref
- get x 3;
val it = ref 1 : int ref
- get x 4;
val it = ref 1 : int ref
- get x 5;
val it = ref 1 : int ref
- (get x 5) := 6;
val it = () : unit
- get x 1;
val it = ref 6 : int ref
- (* Woops!!!*)


- (* list ref, polymorphic ???*)
- val x = ref [];
std_in:19.5-19.14 Error: nongeneric weak type variable
  x : '0Z list ref
- val x = ref [1];
val x = ref [1] : int list ref
- x := [1,2,3];
val it = () : unit
- x := ["a"];
std_in:3.1-3.10 Error: operator and operand don't agree (tycon mismatch)
  operator domain: int list ref * int list
  operand:         int list ref * string list
  in expression:
    := (x,"a" :: nil)
- !x;
val it = [1,2,3] : int list
- 3 :: !x;
val it = [3,1,2,3] : int list



- (* The real thing ? *)
- datatype 'a ring = empty|Node of 'a * 'a ring ref;
datatype 'a  ring
con Node : 'a * 'a ring ref -> 'a ring
con empty : 'a ring
- empty;
val it = empty : 'a ring
- val n1 = Node(1,(ref empty));
val n1 = Node (1,ref empty) : int ring
- val n2 = Node(2,(ref n1));
val n2 = Node (2,ref (Node (#,#))) : int ring
- val (Node(a,t)) = n1;
std_in:3.5-3.20 Warning: binding not exhaustive
        Node (a,t) = ...
val a = 1 : int
val t = ref empty : int ring ref
- t := n2;
val it = () : unit
- (* CLOSE THE KNOT *)
- n1;
val it = Node (1,ref (Node (#,#))) : int ring
- n2;
val it = Node (2,ref (Node (#,#))) : int ring
- val (Node(a,b)) = n1;
std_in:8.5-8.20 Warning: binding not exhaustive
        Node (a,b) = ...
val a = 1 : int
val b = ref (Node (2,ref (Node #))) : int ring ref
- val (Node(c,d)) = !b;
std_in:1.5-1.20 Warning: binding not exhaustive
        Node (c,d) = ...
val c = 2 : int
val d = ref (Node (1,ref (Node #))) : int ring ref
simpson-04% 
script done on Wed Nov 13 16:58:19 1991