my @stack;
while (<RUBY_FILE>) {
    if (/^\s+def (.*)/) {
        push @stack, ['def',$1];
        print;
    } elsif (/^\s+if (.*)/) {
        push @stack, ['if',$1];
        print;
    } elsif (/^\s+end/) {
        my $block = pop @stack;
        if ($block->[0] eq 'def') {
            print "*** definition of $block->[1] ended\n";
        };
    } else {
        # collect, or do something else
        print;
    };
};