IO Monad Considered Harmful

Re:IO Monad Considered Harmful by exDM69 on Friday January 23, 2015 @03:17AM (#8933892)

The issue isn't as great as you portray it to be. You're facing beginner issues and learning a foreign topic, expect to spend some time on it and put in the mental effort and you'll master it in no time. After spending an hour to write "Guess the number" game with and without do notation, you should know enough to be able to write practical programs in Haskell. Yes, an hour for guess the number is a lot, but it's the learning part that takes the time, not just putting a program together.

It makes perfect sense to have do notation and desugaring it to use >>=. For "imperative" programming, do notation makes sense. Other times you'll be writing data processing "pipelines" where using >>= is more convenient. To give an example:

    readQueries inFile >>= readFromDb db >>= writeOutput outFile

The above would be very clumsy to write in do notation (but not too difficult, that's what you'd do in an imperative language). But writing "guess the number" without do notation is also clumsy (but a good learning exercise).

do notation and monad laws may be a foreign concept when coming from an imperative programming background, but it's also a neat an elegant concept that works very well in practice.

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Re:IO Monad Considered Harmful by millstone on Friday January 23, 2015 @03:39AM (#8933938)

I have mastered it, but I have not drunk so much Kool-Aid that I have forgotten what it took!

It sure did not take "no time," and much longer than an hour - longer than any other programming language I have attempted. The biggest stumbling blocks were syntactical. For example, there are three ways to declare a variable (let-in, let, and <-) and if you use the wrong one, you get a very unhelpful error message. The learning was not so much new concepts but instead things like how a "not in scope" error means you used a tab instead of spaces.

I completely agree, the underlying concepts are elegant, and powerful and enlightening and quite amazing. But you can understand the concepts perfectly and still not be able to write a line of Haskell. That's where most tutorials fall short.

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Re:IO Monad Considered Harmful by exDM69 on Friday January 23, 2015 @04:50AM (#8934089)

Perhaps you interpreted me a bit too literally. Of course it takes time for internalizing new and foreign concepts. The lecture, lesson or exercise might only take an hour but it may take days or weeks to grok the concepts. And this might mean a lot of practice.

I certainly remember having a hard time understanding this years ago, and my problem was probably the same as yours - the lack of nice books and tutorials (but things are a bit better now) as well as it all being new and foreign. I don't regret putting in the effort, though.

I also do not like the inconsistency in let-in vs. let (do notation), but I guess there's a good reason for that. <- is not strictly "variable assignment" but it seems superficially similar, though (if comparing to imperative languages).

But I don't think these issues can be "fixed" without turning Haskell into something completely different (e.g. something more like ML). Or do you have a good suggestion how to simplify this without making it worse?

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