countchars.hs

import qualified Data.Set as Set
import Data.Char(toLower)

countChars :: String -> (Int, Int, Int)
countChars s = countChars' (0, 0, 0) (map toLower s)
    where countChars' :: (Int, Int, Int) -> String -> (Int, Int, Int)
          countChars' tup@(v, c, p) [] = tup
          countChars' (v, c, p) (x:xs) | Set.member x vowels = countChars' (v+1, c, p) xs
                                       | Set.member x consonants = countChars' (v, c+1, p) xs
                                       | otherwise = countChars' (v, c, p+1) xs
          vowels = Set.fromDistinctAscList "aeiou"
          consonants = Set.difference (Set.fromDistinctAscList ['a'..'z']) vowels

countLines :: [String] -> (Int, Int, Int)
countLines xs = let addTriples (a, b, c) (a', b', c') = (a+a', b+b', c+c')
                in foldr addTriples (0, 0, 0) $ map countChars xs

main :: IO ()
main = do
    putStr "Name of the file: "
    filename <- getLine
    contents <- readFile filename
    let lines' = lines contents
        (vowels, consonants, punctuation) = countLines lines'
    putStrLn $ "vowels: " ++ (show vowels)
    putStrLn $ "consonants: " ++ (show consonants)
    putStrLn $ "punctuation: " ++ (show punctuation)

OUTPUT

Name of the file: test.txt
vowels: 20
consonants: 39
punctuation: 15

test.txt

Hello, world!
This is just me, talking to myself,
writing a textfile
to read.