KRL uses the "event condition action" pattern. Since there is only space for a single Boolean expression in the condition, KRL adds a prelude section in which preparatory computations can be done. It fits in between the event and condition, setting things up for the conditional action. The prelude begins in line 3 in the rule template shown below.
rule test {
select when sensor heartbeat
pre {
...
}
if condition_is_true then {
send_directive("Heartbeat")
}
fired {
...
} else {
...
}
}
See the child pages of this page for details.