Performative wards

[eelstork]

When passing null arguments to functions returning status, in general intended behaviour is to either cancel or condone the task; sometimes the function itself can make an informed decision; sometimes it makes more sense for the caller to decide.

Example:

task Attack(target, weapon) => Equip(weapon) && Strike(target);

A good implementation of Equip should not fail silently. Then, assuming a bare-handed attack is acceptable, let's use the ? unary operator:

# Will condone Equip (do not invoke; return true) if 'weapon' is null
task Attack(target, weapon) => Equip(weapon?) && Strike(target);

Meanwhile the above function wouldn't be good if it made an agent equip a weapon while no target is defined; in this case, use the ! operator to fail early if a null is passed as target:

# Fail and do not run the task if 'target' is null
task Attack(target!, weapon) => Equip(weapon?) && Strike(target);