As findall/3
and findall/4,
but generates at most N solutions. If
N solutions are returned, this predicate succeeds with a
choice point if Goal has a choice point. Backtracking returns
the next chunk of (at most) N solutions. In addition to
passing a plain integer for N, a term of the form count(N)
is accepted. Using count(N), the size of the next chunk can
be controlled using nb_setarg/3.
The non-deterministic behaviour used to implement the
chunk option in library(pengines). Based on Ciao,
but the Ciao version is deterministic. Portability can be achieved by
wrapping the goal in once/1.
Below are three examples. The first illustrates standard chunking of
answers. The second illustrates that the chunk size can be adjusted
dynamically and the last illustrates that no choice point is left if Goal
leaves no choice-point after the last solution.
?- findnsols(5, I, between(1, 12, I), L).
L = [1, 2, 3, 4, 5] ;
L = [6, 7, 8, 9, 10] ;
L = [11, 12].
?- State = count(2),
findnsols(State, I, between(1, 12, I), L),
nb_setarg(1, State, 5).
State = count(5), L = [1, 2] ;
State = count(5), L = [3, 4, 5, 6, 7] ;
State = count(5), L = [8, 9, 10, 11, 12].
?- findnsols(4, I, between(1, 4, I), L).
L = [1, 2, 3, 4].
[nondet]findnsols(+N,
@Template, :Goal, -List)