{-# LANGUAGE RankNTypes #-}
module ExamplesIO where 


import List 

-- No IO involved in the type, no side-effects then.
f1 :: Eq a => a -> [a] -> ([a], Bool) 
f1 x xs = (take 10 (cycle xs), elem x xs)

-- Here, the type returns an IO Bool. Observe that 
-- the IO computations can do whatever side-effect before 
-- returning the actual boolean value. 
--
-- Once we know it is an IO computation, all the bets are off 
-- if it comes from untrustworthy code!
f2 :: (Show a, Eq a) => Int -> a -> ([a], IO Bool)  
f2 n x = (take n (iterate id x), do putStrLn "Hi!" 
                                    putStrLn "The arguments of the function are" 
                                    putStrLn $ "x = " ++ show x 
                                    putStrLn $ "n = " ++ show n 
                                    return True )