Example: * Lamplighter Three - The flashlight again, but this time with a rechargeable battery and a battery charger that can restore it to full strength. We also use the "warning about the failure" activity to add a more interesting description when the flashlight is about to go out.

Our battery charger is going to be a simple device that includes both a plug and a battery compartment.

    "Lamplighter Three"

    Include Power Sources by Emily Short.

    A light source is a kind of device. Carry out switching on a light source: now the noun is lit. Carry out switching off a light source: now the noun is unlit.

    Salon is a room. A lamp is a fixed in place light source in the Salon. "A lamp [if lit]shines brightly[otherwise]sits[end if] here." The lamp incorporates a PS-plug.

    The flashlight is a light source carried by the player. It incorporates a battery compartment. The player carries a rechargeable battery. The battery drain of the flashlight is 6.

    The Salon contains a wall socket.

    When play begins:
        let spot be a random wall socket in the Salon;
        if spot is a wall socket:
            silently try plugging the lamp into spot.

    The player carries a charger. The charger is a device. The charger incorporates a battery compartment. The charger incorporates a PS-plug. Understand "battery charger" as the charger.

    Instead of examining the charger:
        let cell be a random battery which is in a battery compartment which is part of the charger;
        if cell is not a battery or charger is not wall-powered:
            say "The light on the battery charger is off." instead;
        otherwise if cell is not a rechargeable battery:
            say "The light on the battery charger flashes a warning red." instead;
        otherwise if the cell is fully charged:
            say "The light on the battery charger glows green to indicate a full charge." instead;
        otherwise:
            say "The light on the battery charger glows red to indicate charging."

    Carry out plugging the charger into a wall socket:
        now the charger is in the location.

    Carry out unplugging the charger:
        now the player carries the charger.

    Report inserting a battery into a battery compartment which is part of the charger:
        say "You put [the noun] into [the second noun]. [run paragraph on]";
        try examining the charger instead.

    When play begins:
        let target be a random battery compartment that is part of the charger;
        now the target is open;
        now the target is not openable.

    Rule for warning about the failure of the flashlight:
        if a random battery compartment which is part of the flashlight contains a battery (called the power source):
            let turns remaining be the charge of the power source divided by the battery drain of the flashlight;
            if the turns remaining is 1:
                say "The flashlight is getting appreciably dimmer."

    Test me with "look / turn on lamp / look / unplug lamp / look / turn on lamp / plug in lamp / turn on lamp / unplug lamp / plug lamp into wall socket / i / open flashlight / put battery in flashlight / close battery compartment / turn on flashlight / i / z / z / z / z / z / z / z / z / open flashlight / get battery / put battery in charger / x charger / unplug lamp / plug in charger / x charger / z / z / z / z / z /z / z / x charger / z / z / z / z / z / x charger / put battery in flashlight / turn on flashlight".