|(list type)||creates a mold of a list of a given type|
++list is a standard library function known as “mold generator”.
++list takes one argument, a type, and produces a mold of a list of that type.
As you may recall, a list is a ~(null) terminated series of nouns.
For instance [1 [2 [3 ~]]] is `(list @ud)` and can be written [1 2 3 ~] or ~[1 2 3].