PPT Slide

The predicates bagof and setof are used to gather instances of objects.

We specify a goal, a variable in the goal, and a bag or set name.

For each success of the goal, the constant that matched this variable is gathered into the bag or set.

Example

parent( jan, bet ) .

parent( jan, cat ) .

parent( joe, ann ) .

parent( joe, cat ) .

|?- bagof( Child, parent( jan, Child ), B ) .

B = [ bet, cat ]

read “there exists Who”

|?- bagof( Child, Who^ ( parent ( Who, Child ) ), B ) .

B = [ bet, cat, ann, cat ]

|?- setof( Child, P^( parent ( P, Child ) ), S ) .

S = [ ann, bet, cat ]