Delete empty lists from lists of lists in Prolog

Question

For instance, I have a list:

[ [], [], [], [1], [2,2], [3] ]

How can I delete empty elements from this list?

Answer 1

We can make a predicate that succeeds for empty lists:

empty([]).

Then we can make use of exclude/3 [swi-doc] to filter out elements for which the predicate succeeds:

exclude(empty, [[], [], [], [1], [2,2], [3]], L).

This thus gives us:

?- exclude(empty, [[], [], [], [1], [2,2], [3]], L).
L = [[1], [2, 2], [3]].