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listsml

Is SML hiding elements of the list?

I was testing the following piece of code:

datatype my_int_list = Empty 
                     | Cons of int * my_int_list

fun append (xs, ys) =
    case xs of
        Empty => ys 
      | Cons(x, xs') => Cons(x, append(xs', ys))

If I create list of one element, or of two elements, everything is normal. If I create list of three elements it introduces the # symbol.

- Cons(1, Empty);
val it = Cons (1,Empty) : my_int_list
- Cons(1, Cons(2, Empty));
val it = Cons (1,Cons (2,Empty)) : my_int_list
- Cons(1, Cons(2, Cons(3, Empty)));
val it = Cons (1,Cons (2,Cons #)) : my_int_list

And this is what happens when I try to use the append function:

- val l1 = Cons(1, Cons(2, Cons(3, Empty)));
val l1 = Cons (1,Cons (2,Cons #)) : my_int_list
- val l2 = Cons(4, Cons(5, Cons(6, Empty)));
val l2 = Cons (4,Cons (5,Cons #)) : my_int_list
- append(l1, l2);
val it = Cons (1,Cons (2,Cons #)) : my_int_list

Is this just SML way of telling that there are more elements but it's not gonna bother to print them? If so, can I ask it to print everything? If not, did I do something wrong?

Solution

  • Is this just SML way of telling that there are more elements but it's not gonna bother to print them?

    Yes!

    If so, can I ask it to print everything?

    Yes!

    If not, did I do something wrong?

    No!