setof/3 [ISO]setof(+Template, +Generator, -Set)
Returns the non-empty set Set of all instances of Template such that Generator is provable.
A goal to be proved as if by call/1.
Set is a non-empty set of terms represented as a list of those terms, without
duplicates, in the standard order for terms (see ref-lte-cte).
If there are no instances of Template such that
Generator is satisfied, then setof/3 simply fails.
Obviously, the set to be enumerated should be finite, and should be enumerable by Prolog in finite time. It is possible for the provable instances to contain variables, but in this case Set will only provide an imperfect representation of what is in reality an infinite set.
If Generator is instantiated, but contains uninstantiated
variables that do not also appear in Template, then
setof/3 can succeed nondeterminately, generating alternative
values for Set corresponding to different instantiations of the
free variables of Generator. (It is to allow for such usage that
Set is constrained to be non-empty.)
If Generator is of the form A^B then all the variables in A are treated as being existentially quantified.
Please note: If the instances being gathered contain
attributed variables (see lib-atts) or suspended goals
(see ref-sem-sec), those variables are replaced by brand new
variables, without attributes, in the Set. To retain the
attributes, you can use copy_term/3 (see ref-lte-cpt).
setof/3 can succeed nondeterminately, generating alternative
values for Set corresponding to different instantiations of the
free variables of Generator.
Call errors (see ref-sem-exc).
See findall/3 for examples that illustrate
the differences among findall/3, setof/3, and bagof/3.
findall/3, bagof/3, ^/2, ref-all.