Hello! I'm started to learn Haskell and have some questions. After reading a "Gentle introduction..." I've decided to write a simple program -- a complement to Literate.hs from hugs demos which reads a plain haskell source file and converts it to literate haskell source. The source code of this program follows. Now the questions: - To be able to run it both in Hugs and by GHC I need an `import Data.Char(isSpace) for GHC`. Can this be conditionally included in a source for GHC only? - Am I reinventing the wheel with my `pad` function? Could I use some standard function(s) instead? - What if I'd want to do a more complex processing, like handling {--} comments? The `classify` function analize one line at a time and I'd want too see a surronding context? Should I use another pass, just like for `addblanks`? module Lit where import System(getArgs) -- classification of the haskell source lines data Classified = Program String | Blank | Comment String deriving (Show) classify :: String -> Classified classify ('-':'-':xs) = Comment (dropWhile isSpace xs) classify s | all isSpace s = Blank | otherwise = Program s unclassify :: Classified -> String unclassify (Program s) = "> " ++ s unclassify (Comment s) = s unclassify Blank = [] process :: String -> String process hs = unlines (map unclassify (addblanks (clines hs))) clines hs = map classify (lines hs) -- inserts a blank between a program line and a comment line where needed addblanks :: [Classified] -> [Classified] addblanks = pad needBlank Blank needBlank :: Classified -> Classified -> Bool needBlank (Program p) (Comment c) = True needBlank (Comment c) (Program p) = True needBlank _ _ = False -- inserts a value between those adjanced elements for which -- function p returns True pad :: (a -> a -> Bool) -> a -> [a] -> [a] pad p value [] = [] pad p value (x:[]) = [x] pad p value (x:xs) | p x (head xs) = x:value:rest | otherwise = x:rest where rest = pad p value xs usage err = err ++ "\n" ++ "USAGE: lit <filename>" main :: IO () main = do strs <- getArgs case strs of [] -> ioError (userError (usage "Not enough arguments.")) [str] -> mklit str _ -> ioError (userError (usage "Too many arguments.")) -- takes a filename without suffix, reads a plain haskell source -- and creates a literate haskell source. mklit :: String -> IO () mklit f = do hs <- readFile (f ++ ".hs") writeFile (f ++ ".lhs") (process hs) -- Bst rgrds, M.A.X.: Mechanical Artificial Xenomorph.