トークンのパーサToken parsers

• 似たようなlookfor関数を9つも書くのはいやなので、関数をつくってくれる関数を用意しよう

  Rather than write 9 similar lookfor functions, we'll have another function build them as required:

        sub lookfor {
          my $target = shift;
          my $parser = 
            sub {
              my $tokens = shift;
              my $tok = first($tokens);
              if (type($tok) eq $target) {
                return (value($tok), rest($tokens));
              } else {
               return;           # failure
              }
            };
          return $parser;
        }

• これでlookfor_PLUSのかわりにlookfor("+")と書けるし

  Now instead of lookfor_PLUS we just use lookfor("+")

• lookfor_NUMBERではなくlookfor("NUMBER")と書けばよくなった

  Instead of lookfor_NUMBER we just use lookfor("NUMBER")

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Copyright © 2007 M. J. Dominus