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Design pattern: Command

Description: "Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations."

This pattern can be used with both classes and prototypes.

The simple way to implement this design pattern in Logtalk is to represent commands as parametric object identifiers with the parametric objects implementing the command protocol.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the design pattern sample implementation:

logtalk_load(design_patterns('behavioral/command/loader')).

First, test the basic functionality for light:

light(l1)::turn_on.

<!-- The light(l1) is on true. -->

Commands are represented using parametric object identifiers:

flip_up_command(light(l1))::execute.

<!-- The light(l1) is on true. -->

Use the client/invoker object to store_and_execute commands:

switch::(
                store_and_execute(flip_up_command(light(kitchen))),
                store_and_execute(flip_up_command(coffee_maker))
        ).

<!-- The light(kitchen) is on The coffee_maker is on true. -->

Show the commands history:

switch::history.

<!-- flip_up_command(light(kitchen)) flip_up_command(coffee_maker) true. -->

Reply the commands:

switch::reply_history.

<!-- The light(kitchen) is on The coffee_maker is on true. -->