On Wed, 21 Dec 2005, Daniel Carrera wrote:
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.
x is a String, getLine has type IO String. That's what I was getting at in one of my last e-mails. So you just need something that can read in a string and convert it to an int. Something like let y = (read x) putStrLn $ show $ fib y should work, yes?