Hi everyone, as an exercise for learning Haskell i'm writing a program that converts Ascii Stl files (a simple format for 3D model data) into binary Stl format. In my first attempt i used normal strings and the result was therefore very slow. Now i rewrote the program to use lazy bytestrings instead. But well... it got even slower, so i'm probably doing something terribly wrong ;) Here's what i do (the relevant parts): ... asciiFile <- L.readFile (args!!0) binHandle <- openBinaryFile (args!!1) WriteMode let asciiLines = L.split (c2w '\n') asciiFile ... parseFile binHandle (Normal, tail asciiLines) -- First line contains a comment ... where L is Data.ByteString.Lazy. readFile ought to be lazy so it should not read the whole file into ram at this point. But when i split the lines and pass them to a function, is this still carried out lazily? parseFile processes a line, depending on the StlLineType and then calls itself recursive like this: parseFile :: Handle -> (StlLineType, [L.ByteString]) -> IO () ... parseFile h (Vertex1, s) = do let vals = extractVertex (head s) L.hPutStr h $ runPut (writeFloatArray vals) parseFile h (Vertex2, tail s) ... extractVertex looks like this: extractVertex :: L.ByteString -> [Float] extractVertex s = let fracs = filter (\n -> L.length n > 0) $ L.split (c2w ' ') s in [read (C.unpack(fracs!!1)) :: Float, read (C.unpack(fracs!!2)) :: Float, read (C.unpack(fracs!!3)) :: Float] where C is Data.ByteString.Lazy.Char8. It splits a byte string, filters out the whitespaces and converts certain entries to floats. Maybe unpack is an expensive operation. Is there a better way to convert a Bytestring to float? I know, this is bad Haskell code ;) But where is my grand, obvious misuse of Bytestring? I'm grateful for any suggestion to improve that code. I'm using ghc, version 6.12.1. Thank you, Peter