Word filter to create fancy polyatomic ion mnemonics (http://www2.ucdsb.on.ca/tiss/stretton/database/Mneumonics.html)

filterit.hs

import System.Environment (getArgs)
import Data.List (isPrefixOf, partition)
import Data.Char (toLower)

checkWord :: String -> Int -> Int -> String -> Bool
checkWord begin vowels consonants s = isPrefixOf begin s && vowels == vCount && consonants == cCount
    where isVowel = flip elem "aeiou"
          (vCount, cCount) = let (vs, cs) = partition isVowel s in (length vs, length cs)

main = do
    f <- readFile "wordsEn.txt"
    begin:nVowels:nConsonants:[] <- getArgs

    let matches = filter (checkWord (map toLower begin) (read nVowels) (read nConsonants)) (lines f)
    putStrLn $ show (length matches) ++ " matches:\n--------------"
    mapM_ putStrLn matches