-- a small exercise:
-- how many words are there in a string
 
import Char
 
countWords :: String -> Int
 
data WordFlag = InWord |
                BetweenWords
     deriving Eq
 
type ParseState = (WordFlag, Int)
 
countWordsCore :: String -> ParseState -> (ParseState, String)
 
countWordsCore "" parsestate = (parsestate, "")
 
countWordsCore string parsestate = countWordsCore stringTail (newFlag, newCount)
    where charHead:stringTail = string
          (flag, count) = parsestate
          isHeadAlpha = isAlpha charHead
          newFlag | isHeadAlpha = InWord
                  | otherwise   = BetweenWords
          newCount | isHeadAlpha && (flag == BetweenWords) = count + 1
                   | otherwise                             = count
 
countWords string = count
    where ((_, count), _) = countWordsCore string (BetweenWords, 0)
 
main = do putStrLn "enter a text, complete with Enter"
          string <- getLine
          print (countWords string)

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

Y291bnRXb3Jkc0NvcmUgc3RyaW5nIHBhcnNlc3RhdGUgPSBjb3VudFdvcmRzQ29yZSBzdHJpbmdUYWlsIChuZXdGbGFnLCBuZXdDb3VudCk=

countWordsCore string parsestate = countWordsCore stringTail (newFlag, newCount)