Higher-Order Parsing

Lists

Comma-separated expression lists are common in programming languages
Similarly semicolon-separated statement blocks
Or ...

      sub list_of {
        my ($item, $separator) = @_;
        $separator = lookfor("COMMA") unless defined $separator;
        conc($item, repeat($separator, $item), optional($separator));
      }

Now comma-separated lists:

      $list = conc(lookfor("("),
                   list_of($Expression),
                   lookfor(")"));

Semicolon-separated statement blocks:

      $block = conc(lookfor("{"),
                    list_of($Statement, lookfor(";")),
                    lookfor("}"));