wantarray
            Returns true if the context of the currently executing
            subroutine or "eval" is looking for a list value. Returns false
            if the context is looking for a scalar. Returns the undefined
            value if the context is looking for no value (void context).

                return unless defined wantarray; # don't bother doing more
                my @a = complex_calculation();
                return wantarray ? @a : "@a";

            "wantarray()"'s result is unspecified in the top level of a
            file, in a "BEGIN", "UNITCHECK", "CHECK", "INIT" or "END" block,
            or in a "DESTROY" method.

            This function should have been named wantlist() instead.