fparsec

I'm attempting to parse lisp-style comments from an s-expression language with FParsec. I got a bit of help with parsing single-line comments in this previous thread - How to convert an FParsec parser to parse whitespace While that was resolved, I still need to parse multiline comments. Here's the current code - /// 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 =

For languages with keywords, some special trickery needs to happen to prevent for example "if" from being interpreted as an identifier and "ifSomeVariableName" from becoming keyword "if" followed by identifier "SomeVariableName" in the token stream. For recursive descent and Lex/Yacc, I've simply taken the approach (as per helpful instruction) of transforming the token stream between the lexer and the parser. However, FParsec doesn't really seem do a separate lexer step, so I'm wondering what the best way to deal with this is. Speaking of, it seems like Haskell's Parsec supports a lexer layer,

I've decided to check out FParsec, and tried to write a parser for λ expressions. As it turns out, eagerness makes recursive parsing difficult. How can I solve this? Code: open FParsec type λExpr = | Variable of char | Application of λExpr * λExpr | Lambda of char * λExpr let rec FV = function | Variable v -> Set.singleton v | Application (f, x) -> FV f + FV x | Lambda (x, m) -> FV m - Set.singleton x let Λ0 = FV >> (=) Set.empty let apply f p = parse { let! v = p return f v } let λ e = let expr, exprR = createParserForwardedToRef() let var = lower |> apply Variable let app = tuple2 expr expr