正規表現には*という表記もある。繰り返しの意味だrepeat

• Regexes also have a * notation that means an item can be repeated

• たとえば、こんな風に書けるとよさそうだ

  For example, we might write

 # term → factor repeat( "*" factor )
 $term = $FACTOR - repeat(L("*") - $FACTOR);

• repeatをこれまでのツールで表記するのも難しくはない

  It's not hard to express repeat with what we have already:

 # repeat($p) is:
 
 $p - repeat($p) | $nothing

• でも、関数としてくくり出すこともできる

  But we can wrap this up as a function:

 sub repeat {
 my $p = shift;
 my $repeat_p;
 my $do_repeat_p = sub { $repeat_p->(@_) }; # proxy
 $repeat_p = alt(conc($p, $do_repeat_p), $nothing);
 return $repeat_p;
 }

• Parse::RecDescentでは(s)という表記だ

  Parse::RecDescent provides this with its (s) notation