On 12/17/2012 07:45 AM, Karl Voelker wrote: (...)
Using endBy is not the problem. There are many different solutions:
1. Factor out the common prefix of cell and lastCell, and restructure the file parser to avoid committing to either cell or lastCell until the next input symbol is one which definitively identifies which alternative the parser is looking at.
2. Replace cell and lastCell with a single parser that matches either one. Parse out a list of cellOrLastCell results and then do some post-processing to treat the last one specially.
3. Use the "try" combinator. You apply this combinator to a parser, and get back a parser which consumes no input if it fails. When using this combinator, you should consider whether this will have an unacceptable impact on the performance of your parser. (Performance is one of the reasons Parsec does not just backtrack automatically.)
Ok, I would choose 3 because performance is not the issue and it seems to be the most simple. Still ... I can not do it with "endBy", can I? Do it so: file = do res <- many $ try (do {c <- cell; char ','; return c}) l <- lastCell eof return res cell = many1 (noneOf ",") lastCell = many1 (noneOf "\n") works. But I wonder if I also could have used a clearer combinator from parsec. Regards, Nathan