How to parse comments using FParsec

Question

I am trying to parse lisp comments from s-expression using FParsec. It helped me a little to parse the single-line comments in this previous thread - How to convert the FParsec parser to parse spaces

While this was allowed, I still need to parse multi-line comments. Here the current code is

/// Read whitespace character as a string. let spaceAsStr = anyOf whitespaceChars |>> fun chr -> string chr /// Read a line comment. let lineComment = pchar lineCommentChar >>. restOfLine true /// Read a multiline comment. /// TODO: make multiline comments nest. let multilineComment = between (pstring openMultilineCommentStr) (pstring closeMultilineCommentStr) (charsTillString closeMultilineCommentStr true System.Int32.MaxValue) /// Read whitespace text. let whitespace = lineComment <|> multilineComment <|> spaceAsStr /// Skip any white space characters. let skipWhitespace = skipMany whitespace /// Skip at least one white space character. let skipWhitespace1 = skipMany1 whitespace 

Unfortunately, multi-user analysis never succeeds. Since this is a combinator, I cannot set breakpoints or analyze why it will not work.

Any ideas why this won't work?

Answer 1

Try changing the bool argument for closeMultilineCommentStr to false

 (charsTillString closeMultilineCommentStr false System.Int32.MaxValue) 

Otherwise, it will skip the closeMultilineCommentStr line.

So that it works with nested comments

 let rec multilineComment o= let ign x = charsTillString x false System.Int32.MaxValue between (pstring openMultilineCommentStr) (pstring closeMultilineCommentStr) (attempt (ign openMultilineCommentStr >>. multilineComment >>. ign closeMultilineCommentStr) <|> ign closeMultilineCommentStr) <|o