[Haskell] Type problems

[Donald Bruce Stewart]

Dave:
> I am stumped trying to print values returned from IO functions.
> How to print values returned from getEnv and getEnvironment? 
> 

    import System.Environment

    main = do
        args <- getArgs
        env  <- getEnvironment
        print args
        print env

You evaluate the IO action, extracting its result.

    $ ./a.out hello
    ["hello"]
    [("PATH","/home/dons/bin:/home/dons/bin:/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin:/home/dons/bin:/sbin:/usr/sbin:/usr/local/sbin")....


Note that the do notation is just syntactic sugar for the >>= function,

    getArgs >>= \ args ->
        getEnvironment >>= \ env ->
            print args >>
                print env

It's probably a good idea to read up on monadic IO at some point. The best
references are:

    http://darcs.haskell.org/yaht/yaht.pdf
    http://en.wikibooks.org/wiki/Haskell
    
Also, a lot of articles here:

    http://haskell.org/haskellwiki/Blog_articles

-- Don

P.S. Best asked on the irc channel, you'll get a faster response :-)