Basic parsers

        expression → "(" expression ")" 
                    | term ("+" expression | nothing)

• The simplest parser is the one that corresponds to nothing

• It consumes no tokens and always succeeds:

        sub nothing {
          my $tokens = shift;
          return (undef, $tokens);
        }

• This parser function gets a token list

  • It examines the tokens

  • Returns a value and a new token list

• The undef here is a dummy value

  • The new token list is the same as the old one

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Copyright © 2007 M. J. Dominus