Add an "else" branch to the "when" conditional

[marvelous]

when toto == 1 do
    callsub start_moving
else/otherwise
    callsub stop_moving
end

It should only get executed when the condition goes from true to false. A workaround is to add an other when with a negated condition.

[stephanemagnenat]

It makes sense, and won't be too hard to implement. I suggest to use else to avoid adding a new keyword.

P.R. including proper unit tests welcome!