🚀 go-pugleaf

[I tried to mail you, but somehow my mailer choked on your address]

Your problem was somewhat underspecified. I assumed that you did not
want any variables to become instantiated as a result of a call to
good/1. The trick I use is List \= a which means that List must not be
unifiable with atom a (in particular, it can't be a variable). I
tested the following with sbprolog:

good(Lists) :- are_lists(Lists,Length).

is_list(List,Length) :- List \= a, List = [], Length = 0.
is_list(List,Length) :- List \= a, List = [Head|Tail],
	is_list(Tail,TailLength), Length is 1 + TailLength.

are_lists(Lists,Length) :- Lists \= a, Lists = [].
are_lists(Lists,Length) :- Lists \= a, Lists = [Head|Tail],
	is_list(Head,Length), are_lists(Tail,Length).


--Denys