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copied!<p>You can speed it up by using <code>ByteString</code>s, e.g.</p> <pre><code>module Main (main) where import System.Environment (getArgs) import qualified Data.ByteString.Lazy.Char8 as C import Data.Char main :: IO () main = do args <- getArgs mapM_ doFile args doFile :: FilePath -> IO () doFile file = do bs <- C.readFile file let tups = buildTups 0 [] $ C.dropWhile (not . isDigit) bs print (length tups) buildTups :: Int -> [Int] -> C.ByteString -> [(Int,Int,Int,Int,Int,Int)] buildTups 6 acc bs = tuplify6 acc : buildTups 0 [] bs buildTups k acc bs | C.null bs = if k == 0 then [] else error ("Bad file format " ++ show k) | otherwise = case C.readInt bs of Just (i,rm) -> buildTups (k+1) (i:acc) $ C.dropWhile (not . isDigit) rm Nothing -> error ("No Int found: " ++ show (C.take 100 bs)) tuplify6:: [a] -> (a, a, a, a, a, a) tuplify6 [l, m, n, o, p, q] = (l, m, n, o, p, q) </code></pre> <p>runs pretty fast:</p> <pre><code>$ time ./fileParse IntList 200000 real 0m0.119s user 0m0.115s sys 0m0.003s </code></pre> <p>for an 8.1 MiB file.</p> <p><del>On the other hand, using <code>String</code>s and your conversion (with a couple of <code>seq</code>s to force evaluation) also took only 0.66s, so the bulk of the time seems to be spent not parsing, but working with the result.</del></p> <p>Oops, missed a <code>seq</code> so the <code>read</code>s were not actually evaluated for the <code>String</code> version. Fixing that, <code>String</code> + <code>read</code> takes about four seconds, a bit above one with the custom <code>Int</code> parser from @Rotsor's comment</p> <pre><code>foldl' (\a c -> 10*a + fromEnum c - fromEnum '0') 0 </code></pre> <p>so parsing apparently did take a significant amount of the time.</p>

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