filter : ('a -> bool) -> 'a list -> 'a list

SYNOPSIS: Filters a list to the sublist of elements satisfying a predicate.
DESCRIPTION: 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.
FAILURE CONDITIONS: Fails if the predicate fails on any element.
SEE ALSO: mapfilter, partition, remove.