define_events/5 — The Logtalk Handbook v3.47.0 documentation

# `define_events/5`

## Description

    define_events(Event, Object, Message, Sender, Monitor)

Defines a new set of events. The two types of events are represented by the atoms `before` and `after`. When the predicate is called with the first argument unbound, both types of events are defined. The object `Monitor` must define the event handler methods required by the `Event` argument.

## Modes and number of proofs

    define_events(@term, @term, @term, @term, +object_identifier) - one

## Errors

`Event` is neither a variable nor a valid event identifier:
`type_error(event, Event)`
`Object` is neither a variable nor a valid object identifier:
`type_error(object_identifier, Object)`
`Message` is neither a variable nor a callable term:
`type_error(callable, Message)`
`Sender` is neither a variable nor a valid object identifier:
`type_error(object_identifier, Sender)`
`Monitor` is a variable:
`instantiation_error`
`Monitor` is neither a variable nor a valid object identifier:
`type_error(object_identifier, Monitor)`
`Monitor` does not define the required `before/3` method:
`existence_error(procedure, before/3)`
`Monitor` does not define the required `after/3` method:
`existence_error(procedure, after/3)`

## Examples

    % define "debugger" as a monitor for member/2 messages
    % sent to the "list" object:
    | ?- define_events(_, list, member(_, _), _ , debugger).

See also

abolish_events/5, current_event/5, before/3, after/3