filterLib.filter : ('a -> bool) -> 'a list -> 'a list
Filters a list to the sublist of elements satisfying a predicate.
filter P l applies P to every element of
l, returning a list of those that satisfy P,
in the order they appeared in the original list.
If P x fails for some element x of
l.
Identical to List.filter from the Standard ML Basis
Library.