import Prelude hiding (putStr,getLine)

main1 = putStr "Hi" >> putStr "Hi"

main2 = let x = putStr "Hi"
        in x >> x

main3 = let actions = repeat (putStr "Hi")
        in actions!!3 >> actions!!99

-- Applies an I/O action twice:
dupAct :: IO a -> IO a
dupAct act = act >> act

main4 = dupAct (putStr "Hi")

-- Applies an I/O action multiple times:
multAct :: Int -> IO a -> IO a
multAct n act = foldr1 (>>) (take n (repeat act))

main5 = multAct 2 (putStr "Hi")


fac :: Integer -> Integer
fac n = if n==0 then 1 else n*fac(n-1)

printFac10 :: IO ()
--printFac10 = putStr (show (fac 10))
printFac10 = print (fac 10)
             
putStr :: String -> IO ()
putStr []     = return ()
putStr (c:cs) = putChar c >> putStr cs

-- Reads a line from the keyboard
getLine' :: IO String
getLine' = getChar >>= \c -> if c=='\n'
                              then return ""
                              else getLine' >>= \cs -> return (c:cs)

-- Reads a line from the keyboard
getLine :: IO String
getLine = do c <- getChar
             if c=='\n'
               then return ""
               else do cs <- getLine
                       return (c:cs)

-- Print intermediate result of factorial computation
facPrint :: Integer -> IO Integer
facPrint n = if n==0 then return 1
                     else do f1 <- facPrint(n-1)
                             print (n-1, f1)
                             return (n*f1)
                               
mainFac :: IO ()
mainFac = do putStr "n = "
             inp <- getLine
             f <- facPrint (read inp)
             putStrLn ("The factorial of " ++ inp ++ " is " ++ show f)

-- Prints number of a lines of a file:
printFileLines :: String -> IO ()
printFileLines f = readFile f >>= print . length . lines

-- Prints number of a empty lines of a file:
printFileELines :: String -> IO ()
printFileELines f = readFile f >>= print . length . filter (all (==' ')) . lines