free/1 (i)
This predicate succeeds if the supplied argument is a free Prova variable.
The following example test010.prova shows how the free predicate can be used in th eprocess of constructing a sorted tree representation of an initially unsorted list.
% Sort the list provided :- solve(sort([7,3,6,1,4,5],L)). insert_a(Val,t(Val,_,_)):-!. insert_a(Val,t(Val1,Tree,_)):- Val<Val1, !, insert_a(Val,Tree). insert_a(Val,t(_,_,Tree)):- insert_a(Val,Tree). instree([],_). instree([H|T],Tree):- insert_a(H,Tree), instree(T,Tree). treemembers(_,T):- free(T), !, fail(). treemembers(X,t(_,L,_)):- treemembers(X,L). treemembers(X,t(X,_,_)). treemembers(X,t(_,_,R)):- treemembers(X,R). sort(L,L1):- instree(L,Tree), findall(X,treemembers(X,Tree),L1).
This returns:
L=[1, 3, 4, 5, 6, 7]