Checks that all the captures of the case are present in the case.
Checks that all the captures of the case are present in the case.
Sometimes, because of earlier substitutions of an abstract type constructor, we can end up with patterns that do not mention all their captures anymore. This can happen even when the body still refers to these missing captures. In that case, we must always consider the case to be unmatchable, i.e., to become Stuck.