Re: [Haskell-cafe] IO is a bad example for Monads

9 Dec 2007

      Am Sonntag, 9. Dezember 2007 23:35 schrieb Ketil Malde:
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Daniel Fischer  writes:
...
...
...
IO is important because you can't write any real program without using
it.
Ouch!  I get awfully discouraged when I read statements like this
one.
I think Lennart was referring to that, you HAVE to know a little IO to
write programmes, at least getArgs, getLine, putStr(Ln), readFile,
writeFile, appendFile. And therefore some use of the IO monad has to be
taught relatively early.
Emphasis on *use*, introduce the concept of monads not before lists, Maybe and 
Either.
...
Well, I guess you could get pretty far using 'interact' - far enough
in an educational setting to do lists and Maybe, and then monads,
before introducing monadic IO.
-k
Pretty far, yes, and in an educational setting, at a university, it is quite 
common, I believe, to use an interpreter for a while, not producing 
executables (that's how I met Haskell, write pure functions and type 
expressions at the Hugs prompt). But what about a tutorial for programmers?
How would you do

main = do
    putStrLn "Please enter your name."
    name <- getLine
    putStrLn $ "Hello " ++ name ++ ", nice to meet you."

in that setting?
I doubt you could keep many interested without telling them how to create 
standalone programmes, including reading input from stdin and printing output 
to stdout.

Cheers,
Daniel