Higher-Order Parsing

Parsers

With this definition, a complete definition of atom() is:

        $atom = alt(lookfor("NUMBER"),
                    lookfor("VAR"),
                    conc(lookfor("FUNC"),
                         lookfor("("),
                         $Expression,
                         lookfor(")"),
                        ));

Similarly, here's factor():

     #  factor → atom ("^" NUMBER | nothing)

     $factor = conc($Atom, alt(conc(lookfor("^"), 
                                    lookfor("NUMBER")),
                               \&nothing));

Here's term():

     #  term → factor ("*" term | nothing)

     $term = conc($Factor, alt(conc(lookfor("*"), $Term),
                               \&nothing));