setof/3 — Logtalk 3.100.1

built-in method

# `setof/3`

## Description

    setof(Template, Goal, List)

Collects a set of solutions for the goal for each set of instantiations of the free variables in the goal. The solutions are sorted using standard term order. The free variables in the goal are the variables that occur in the goal but not in the template. Free variables can be ignored, however, by using the `^/2` existential qualifier. For example, if `T` is term containing all the free variables that we want to ignore, we can write `T^Goal`. Note that the term `T` can be written as `V1^V2^...`.

When there are free variables, this method is re-executable on backtracking. This method fails when there are no solutions, never returning an empty list.

This built-in meta-predicate is declared as a private method and thus cannot be used as a message to an object.

## Meta-predicate template

    setof(*, ^, *)

## Modes and number of proofs

    setof(@term, +callable, -list) - zero_or_more

## Errors

`Goal` is a variable:
`instantiation_error`
`Goal` is neither a variable nor a callable term:
`type_error(callable, Goal)`
`Goal` is a call to a non-existing predicate:
`existence_error(procedure, Predicate)`

## Examples

To find a set of solutions in the context of the object or category containing the call:
`setof(Template, Goal, List)`
To find a set of solutions of sending a message to self:
`setof(Template, ::Message, List)`
To find a set of solutions of sending a message to an explicit object:
`setof(Template, Object::Message, List)`

See also

bagof/3, findall/3, findall/4, forall/2