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

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Copyright © 2007 M. J. Dominus