wchogg:
Hey Haskell, So for a fairly inane reason, I ended up taking a couple of minutes and writing a program that would spit out, to the console, the number of lines in a file. Off the top of my head, I came up with this which worked fine with files that had 100k lines:
main = do path <- liftM head $ getArgs h <- openFile path ReadMode n <- execStateT (countLines h) 0 print n
untilM :: Monad m => (a -> m Bool) -> (a -> m ()) -> a -> m () untilM cond action val = do truthy <- cond val if truthy then return () else action val >> (untilM cond action val)
countLines :: Handle -> StateT Int IO () countLines = untilM (\h -> lift $ hIsEOF h) (\h -> do lift $ hGetLine h modify (+1))
If this makes anyone cringe or cry "you're doing it wrong", I'd actually like to hear it. I never really share my projects, so I don't know how idiosyncratic my style is.
This makes me cry. import System.Environment import qualified Data.ByteString.Lazy.Char8 as B main = do [f] <- getArgs s <- B.readFile f print (B.count '\n' s) Compile it. $ ghc -O2 --make A.hs $ time ./A /usr/share/dict/words 52848 ./A /usr/share/dict/words 0.00s user 0.00s system 93% cpu 0.007 total Against standard tools: $ time wc -l /usr/share/dict/words 52848 /usr/share/dict/words wc -l /usr/share/dict/words 0.01s user 0.00s system 88% cpu 0.008 total -- Don