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Comment by JoshTriplett | Hacker News Reader

> Here's how I might write that today, without using do notation: `getLine >>= (return . (++) "Hello, ") >>= putStrLn`.

Don't write point-free code here. Here's a fairly simple version:

    getLine >>= \name -> putStrLn ("Hello, " ++ name)

The only novel thing there is the >>= operator itself. You don't even have to introduce return there; you can introduce return later.

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Which can then be made to look exactly like the

  getLine >>= putStrLn

case by doing

  greet name = putStrLn ("Hello, " ++ name)
  main = getLine >>= greet

(Edited to include the definition of main)

This is a nice approach. Thanks to all of you in this thread. I think I'll try something like this when I introduce Haskell I/O in my Programming Languages class in a month or two.

If this is meant to be under main, you need a "let":

    main = do
      let greet name = putStrLn ("Hello, " ++ name)
      getLine >>= greet

For whatever reason, I didn't learn about the magic let syntax in do-notation until relatively late. Anyways this is very elegant, but not something I could have generated early on, especially because it mixes two different sequencing syntaxes (do-notation and >>=).

The 'do' is superfluous.

It would be much better as

    main = let greet name = putStrLn ("Hello, " ++ name)
                in getLine >>= greet

You can use "fmap" to make this nicer (but that introduces yet another concept). If you use hlint on the program above, you it will tell you to use fmap instead.

    fmap ("Hello, " ++) getLine >>= putStrLn

I learned this because hlint suggested it to me. Using hlint is a very good idea, even for beginners.

For a simple "greet" program, this isn't perhaps any neater or cleaner but fmap is a powerful tool with lots of practical uses.

Thanks, that's much better than what I wrote. Still I think that's a big jump for most programmers - it certainly was for me.

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