Hello. I've rewritten the source position handing of parsec so that you can now use different position markers such as commandline arguments. You can find it with a demo application here: (Still very untested) http://www.mawercer.de/marcweber/haskell/fparsec/ Do you think this would be useful merging back (after fixing some small bugs like missing spaces in error message and adding some more documentation) ? Example application: ---------------------------------------------------- module Main where import Data.List import Text.ParserCombinators.Parsec.Prim import Text.ParserCombinators.Parsec.Combinator import Text.ParserCombinators.Parsec.Token import Text.ParserCombinators.Parsec.Char import Text.ParserCombinators.Parsec.Argument usage = unlines [ "cat <file> <file> (- means stdin/out)" , "tac <file> <file> (- means stdin/out)" , "calc 3 + 7 \\* 8 ... <- shell escape" ] cat :: ( String -> String ) -> String -> ArgParser () (IO ()) cat f s = do expectToken s input <- inputFile output <- outputFile return $ input >>= output . f calc :: ArgParser () (IO ()) calc = expectToken "calc" >> sum >>= return . print where sum = fmap (foldr1 (+)) (sepBy product (expectToken "+") ) product =fmap (foldr1 (*)) (sepBy value (expectToken "*")) value = intArg parser = choice [ cat id "cat" -- cat , cat (unlines . map reverse . lines) "tac" -- cat but reverse lines , calc -- simple calculator, only knows how to do + and * operations ] main = do action <- handleArgs parser () usage action ---------------------------------------------------- Marc Weber