actions.pm question

        my $invocant  := $( $/[0] );
        my $call      := $( $/[1] );

        # [...]

        # We only want to evaluate invocant once; stash it in a register.
        $call.unshift(PAST::Op.new(
            :pasttype('bind'),
            PAST::Var.new(
                :name('detemp'),
                :scope('register'),
                :isdecl(1)
            ),
            $invocant
        ));

# Question: if I know that $invocant will be '$_', how do I change the above?
# Does the string '$_' suffice?