Reusable Rules via Functions

Quite often, there are rules with all the same logic, but operating on different items and with different parameters. Using lambda expressions, it is in fact possible to specify reusable and parameterizable functions. The example below can be used to control rollershutters:

• S_[name]_up is a switch (input) item to move it up
• S_[name]_down is a switch (input) item to move it down
• R_[name]_up is the switch item that actually moves it up
• R_[name]_down is the switch item that actually moves it down

Some constants and functions are defined at the top:

// total runtime of the rollershutters
val int ROLLO_TIMEOUT = 20

// timers to switch it off after the timeout
val java.util.Map<String, org.openhab.model.script.actions.Timer> rolloTimers = newHashMap

// lambda expression that can be used as a function (here: with 5 parameters)
val org.eclipse.xtext.xbase.lib.Functions$Function5 rolloLogic = [
	org.openhab.core.library.items.SwitchItem relayItem,
	org.openhab.core.library.items.SwitchItem relayItemOpposite,
	java.util.Map<String, org.openhab.model.script.actions.Timer> timers,
	String timerKey, int timeout |
		// if current state is off
		if (relayItem.state == OFF) {
			// if opposite state is also off
			if (relayItemOpposite.state == OFF) {
				// switch it on!
				relayItem.sendCommand(ON)
				// if there is already a timer, cancel it
				timers.get(timerKey)?.cancel
				// now create a new timer for switching off
				timers.put(timerKey, createTimer(now.plusSeconds(timeout)) [|
					// switch it off afterwards, if it is not already off
					if (relayItem.state == ON)
						relayItem.sendCommand(OFF)
					// remove timer from map because nothing is ON anymore
					timers.remove(timerKey)
				])
			} else { // opposite is on
				// switch opposite off!
				relayItemOpposite.sendCommand(OFF)
			}
		} else { // it is already on
			// switch it off
			relayItem.sendCommand(OFF)
		}
]

And the actual rules simply call the function rolloLogic with their specific parameters:

rule "rollo kitchen up"
when Item S_Kitchen_up changed to ON then
	rolloLogic.apply(R_Kitchen_up, R_Kitchen_down, rolloTimers, "Kitchen", ROLLO_TIMEOUT)
end
rule "rollo kitchen down"
when Item S_Kitchen_down changed to ON then
	rolloLogic.apply(R_Kitchen_down, R_Kitchen_up, rolloTimers, "Kitchen", ROLLO_TIMEOUT)
end
rule "rollo bathroom up"
when Item S_Bathroom_up changed to ON then
	rolloLogic.apply(R_Bathroom_up, R_Bathroom_down, rolloTimers, "Bathroom", ROLLO_TIMEOUT)
end
rule "rollo bathroom down"
when Item S_Bathroom_down changed to ON then
	rolloLogic.apply(R_Bathroom_down, R_Bathroom_up, rolloTimers, "Bathroom", ROLLO_TIMEOUT)
end

This should simplify many rule definitions :-)