On 21/12/05, Daniel Carrera
Thanks for all the help. I think things are much clearer now. And this bit:
main = do putStrLn "Hello, what is your name?" name <- getLine putStrLn ("Hello, " ++ name ++ "!")
Looks quite straight forward.
I just wrote my very first IO program with Haskell: --//-- main = do x <- getLine putStrLn( show(length x) ) --//--
That's not so scary. The next thing I need to figure out is how to act on the input data itself (not just its length). For example, if I wanted a program to output the nth element of the fibonacci sequence: --//-- $ ./fib 12 144 --//--
My first inclination would be to write it as: --//-- main = do x <- getLine putStrLn( show(fib x) ) --//--
Of course that won't work because x is an IO String and 'fib' wants an Int. To it looks like I need to do a conversion "IO a -> b" but from what Cale said, that's not possible because it would defeat the referential transparency of Haskell.
Actually, you're closer than you think here. x is actually of type String! The problem is just that fib wants a number, so you need to read the string: main = do x <- getLine putStrLn (show (fib (read x))) There's a handy name for the composite (putStrLn . show) called 'print', so you can write: main = do x <- getLine print (fib (read x))) Cheers! - Cale