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));