module L03A where
import Data.List
import Data.Char

-- **** 
-- Small examples of IO
-- writeFile

-- * Building instructions vs running instructions
-- instructions with results:

-- readFile

-- building complex instructions from simple ones

copyFile :: FilePath -> FilePath -> IO()
copyFile fromFile toFile = 
   do c <- readFile fromFile 
      writeFile toFile c

-- var <- expr 
-- var :: a  expr :: IO 

-- find longest Word in "/usr/share/dict/words"
longest :: IO String
longest = do 
        wlist <- readFile "/usr/share/dict/words"
        return (long wlist)

  where long :: String -> String
        long  = snd . maximum . map (\w -> (length w, w)) . words

-- dotwice

dotwice :: IO a -> IO (a,a)
dotwice i = do 
        a1 <- i
        a2 <- i
        return (a1,a2)

dont :: IO a -> IO ()
dont i = return ()

test :: IO Int
test = do 
     return 42
     return 0

-- sequence_ 
mySequence_ :: [IO a] -> IO ()
mySequence_ []     = return ()
mySequence_ (i:is) = 
  do i 
     mySequence_ is
 -- i >> mySequence_ is

-- sequence
mySequence :: [IO a] -> IO [a]
mySequence [] = return []
mySequence (i:is) = 
  do a <- i
     as <- mySequence is
     return (a:as)

-- Exercises: Define the following functions: 
copyAll :: [FilePath] -> FilePath -> IO()
copyAll fromFiles toFile = undefined
  -- hint: sequence :: [IO a] -> IO [a]   
  --       map :: (a -> b) -> [a] -> [b]

forLoop :: [a] -> (a -> IO ()) -> IO ()
forLoop = undefined 
-- e.g. forLoop [1..10] print 
-- will print numbers from 1 to 10.