Functional Programming - class 8

kent-class8.hs

{-
    IO operations can be composed through >>=, which is:

        (>>=) :: IO a -> (a -> IO b) -> IO b
    
    The other building block for IOs is the return operation:

        return :: a -> IO a
-}

foo :: IO ()
foo =
    putStrLn "Type a number:" >>= (\() ->
        getLine >>= (\x ->
            putStrLn "Type another number:" >>= (\() ->
                getLine >>= (\y ->
                    putStrLn (show (read x + read y))))))

bar :: IO Integer
bar = do
    putStrLn "Type a number:"
    x <- getLine
    putStrLn "Type another number:"
    y <- getLine
    let n = read x + read y
    putStrLn $ show n
    return n

baz :: IO ()
baz = do
    -- Call the action bar once, binding the result into n
    n <- bar
    -- Call it a second time, biding the result into m
    m <- bar
    -- We have asked the user for four numbers now,
    -- So just sum them all up and show it to him!
    putStrLn "Final result:"
    putStrLn $ show (n + m)