built-in method

once/1

Description

once(Goal)

This predicate behaves as call(Goal) but it is not re-executable. This built-in meta-predicate is declared as a private method and thus cannot be used as a message to an object.

This meta-predicate is opaque to cuts in its argument.

Modes and number of proofs

once(+callable) - zero_or_one

Errors

Goal is a variable:

instantiation_error

Goal is neither a variable nor a callable term:

type_error(callable, Goal)

Examples

Call a goal deterministically in the context of the object or category containing the call:

once(Goal)

To send a goal as a non-backtracable message to self:

once(::Goal)

To send a goal as a non-backtracable message to an explicit object:

once(Object::Goal)

See also

call/1-N, ignore/1, (\+)/1