reference parameters

<>
? ??listput
listput( list,x,{n}):

    Sets the n-th element of the list list (which must be of type 
t_LIST) equal to x. If n is omitted, or greater than the list length, 
appends x. The function returns the inserted element.

    ? L = List();
    ? listput(~L, 1)
    %2 = 1
    ? listput(~L, 2)
    %3 = 2
    ? L
    %4 = List([1, 2])

Note the ~ L: this means that the function is called with a reference to 
L and changes L in place.
</>

Is that explicit reference notation still relevant?

-- Ruud