Higher-Order Parsing

パーサParsers

この関数を使うと、atomの完全な定義はこうなる
With this definition, a complete definition of atom is:

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

$factorもほとんど同じ
Similarly, here's $factor:

     #  factor → atom ("^" NUMBER | nothing)
     
     $factor = conc($ATOM, alt(conc(lookfor("^"), 
                                    lookfor("NUMBER")),
                               \￢hing));

$termはこう
Here's $term:

     #  term → factor ("*" term | nothing)
     
     $term = conc($FACTOR, alt(conc(lookfor("*"), $TERM),
                               \&nothing));