Higher-Order Parsing

Parsers

     # expression → "(" expression ")" 
     #             | term ("+" expression | nothing)

     $expression = alt(conc(lookfor("(")),
                            $Expression,
                            lookfor(")"),

                       conc($Term,
                            alt(conc(lookfor("+"), $Expression),
                                \&nothing));

This doesn't look great, but:
1. When you consider how much it's doing, it's amazingly brief, and
2. We can use operator overloading and rewrite it as:

      $expression = L("(") - $Expression - L(")")
                  | $Term - (L("+") - $Expression | $nothing);