A modern functional language such as SML has a similar form:

<pre>
fun sum l =
    if null(l) then 0 else hd(l) + sum(tl(l));
</pre>

However SML has a sophisticated and rigorous static type system, due to
Hindley and Milner.


<a>A more direct descendent of POP-2 is POP-11:

<pre>
define sum(l);
  if null(l) then 0 else hd(l) + sum(tl(l))
  endif
enddefine;
</pre>

POP-11 is the core language of the POPLOG system, which provides integrated
implementations of SML, Prolog and Common Lisp, in addition to POP-11.