Not If

not_if

not_if allows prevents execution of rules when result is false and prevents when true

 rule 'Set OutsideDimmer to 50% if LightSwtich turned on and OtherSwitch is OFF' do
        changed LightSwitch, to: ON
        run { OutsideDimmer << 50 }
        not_if { OtherSwitch == ON }
      end

Because not_if uses ‘truthy?’ on non-block objects the above rule can also be written like this:

rule 'Set OutsideDimmer to 50% if LightSwtich turned on and OtherSwitch is OFF' do
  changed LightSwitch, to: ON
  run { OutsideDimmer << 50 }
  not_if OtherSwitch
end

Multiple not_if statements can be used and if any of them are not satisfied the rule will not run.

rule 'Set OutsideDimmer to 50% if LightSwtich turned on and OtherSwitch is OFF and Door is not CLOSED' do
  changed LightSwitch, to: ON
  run { OutsideDimmer << 50 }
  not_if OtherSwitch
  not_if { Door == CLOSED }
end