stupid Haskell letter counter

stupid_letter_counter.hs

import Data.Char
import Debug.Trace
import System.IO

main :: IO()
main = do
  hSetBuffering stdin NoBuffering
  putStrLn "Sample: counting words with a given letter"
  putStrLn "Input letter to count:"
  letter <- getChar
  hFlush stdout
  putStrLn ""
  putStrLn "Input string to scan:"
  line <- getLine
  putStrLn "Processing..."
  putStrLn $ countWordsWithLetter letter line


countWordsWithLetter :: Char -> String -> String
countWordsWithLetter letter line =
  "Counted " ++ show result ++ " words with letter " ++ show letter
  where
    reduce = countLetters letter
    reduction = foldl reduce initialReduction line
    result = totalCount reduction

data Reduction =  Reduction { totalCount :: Integer, skipNextLetter :: Bool} deriving (Show)
initialReduction :: Reduction
initialReduction = Reduction {totalCount=0, skipNextLetter=False}

type Reduce = Reduction -> Char -> Reduction
countLetters :: Char -> Reduce
-- the following line provides a debug trace, eventually add --v arg to turn on or off
countLetters _ reduction letter | trace ("letter: " ++ show letter ++ " " ++ show reduction) False = undefined
countLetters target (Reduction count skip) letter
  | isSpace letter = Reduction count False
  | skip = Reduction count skip
  | toLower letter == target = Reduction (count+1) True
  | otherwise = Reduction count skip