Question

In Parse::RecDescent, how do I effectively ignore C++/Java style comments? This includes single-line (‘//’ until the end of the line) and multi-line (/everything between here/).

Answer 1

<skip> defines what the parser considers whitespace.

parse: <skip: qr{(?xs:
          (?: \s+                       # Whitespace
          |   /[*] (?:(?![*]/).)* [*]/  # Inline comment
          |   // [^\n]* \n?             # End of line comment
          )
       )*}>
       main_rule
       /\Z/
       { $item[2] }

Unlike Nate Glenn’s solution, mine

• Doesn’t set a global variable affecting all parsers.
• Doesn’t use needless captures.
• Doesn’t use the non-greedy modifier. (He used the non-greedy modifier to make sure certain characters aren’t matched at certain spots, but the non-greedy modifier doesn’t guarantee that.)

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Note: (?:(?!STRING).)* is to (?:STRING) as [^CHAR] is to CHAR.