Functions Operating on the IO Monad
putChar :: Char -> IO () getChar :: IO Char (>>) :: IO a -> IO b -> IO b return :: a -> IO a
❍❍
❍✟
✟✟
b IO2
❍❍
❍✟
✟✟
IO1 IO2 b
❍❍
❍✟
✟✟
a
IO1 >> =
(>>=) :: IO a -> (a -> IO b) -> IO b
❍❍
❍✟
✟a✟
IO1 ❍✟❍❍✟
✟b IO2
❍❍
❍✟
✟✟ a ❍✟❍❍✟
✟a
IO1 ❍✟❍❍✟
✟b IO2
❍❍
❍✟
✟✟ a
>>= =
getChar >> return () reads a character and ignores it
getChar >>= putChar reads a character and prints it on the screen
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do-Notation
gets :: Int -> IO String gets n = if n <= 0
then return []
else getChar >>= \x ->
gets (n-1) >>= \xs ->
return (x:xs) p >>= \x ->
q >>= \y ->
r
can be written as
do x <- p y <- q r
gets :: Int -> IO String
gets n = if n <= 0 then return []
else do x <- getChar
xs <- gets (n-1) return (x:xs)
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