There are very few things in the world of CS/programming where I can't follow along and grok what's going on, especially when laid out in a tutorial form like this. The fact that I was totally lost when reading this is not a good sign when you're trying to get people to adopt your school of thought.
Haskell is difficult to explain because it has many terms, vocabulary, and syntax that are not familiar to people. It's ML-style syntax doesn't help.
Most tutorials targeting Haskell beginners implicitly assume the readers already know the Haskell syntax, terms, definition, etc, and go right ahead to explain the advance concepts like functor, applicative, or monad. It's like teaching them how to fly before they know how to walk, in the Haskell land. No wonder Haskell beginners are frustrated with any of the monad tutorial.
The thing is. Stop. Stop telling beginners what monad is. Just show them the basics in Haskell and get something useful going. Get them to write and use Haskell programs. When the need arise, they will look into what monad is. Programmers have used STL plenty without knowing the internals of C++ templates. Same thing can be done with monad.
> When the need arise, they will look into what monad is.
I couldn't have said it any better. This is the exact scenario that this post is aimed at.
That's probably because most of the tutorials you've followed have adopted an imperative style of programming. It is easy for you to follow along because it really isn't all that different from what you are accustomed to. Functional programming really is a different beast entirely. It's often said (though I remain skeptical) that it's actually easier to learn functional programming as a non-programmer than to un-learn your imperative programming tendencies.
>The fact that I was totally lost when reading this is not a good sign when you're trying to get people to adopt your school of thought.
I don't think that's a fair assessment. You could say the same thing about starting from functional programming and switching to imperative; some people actually do this! They find the idea of mutating a variable to be completely counter-intuitive!
As someone who'd done reasonably well with both and had thought of them as heavily overlapping areas, I thought this was interesting, so I tried to poke at this a bit.
One of the concepts I got back from a talented classmate was basically a complaint about mutable variables -- that in an algebraic description of relationships for a given system what we call "variables" are less variable and more "unknowns" which represent fixed if unidentified quantities. Others similarly noted there was something absurd about writing out equations like "x = x + 2".
The trick is to stop reading that line (in your head) as "x is equal to x plus two", but instead "x is assigned the value of x plus two".
That's one potential takeaway, but when I turned over the complaint in my mind, this was arguably another way of complaining about mutability.
Also, given the timing, it's pretty likely that one of the languages they'd learned was Pascal: that was the language of the first few CS classes at my school in the 90s, it was also the language of any high school curriculum that led to the AP exam, and Borland's Pascal products were still pretty popular PC dev environments.
They could've also been unlucky and received their first exposure by choosing to do a numerical analysis class in Fortran or C, of course. :/
Source: all my classmates.
The notion of mutation is implicit in the definition of "variable."
So you don't change it during one exercise, but you can and certainly will change it when you change the exercise to another one with the same principle.
That's not analogous at all to mutation.
For example, if you integrate x^2 dx from x=0 to 10, x changes continuously.
It's clear that x is not fixed to any particular value.
foo x = x * 2
The series of additions can also be infinite, in which case it would be quite difficult to expand fully, but that doesn't prevent you from doing mathematics with it.
At the end of the day, you adopt a new way of thinking that is incredibly clarifying for all programming. One simple thing is that it allows you to "see" where state, re-entry, evaluation, IO, and failure are happening in a program---things that you are blind to when you're used to languages where the answer is "always".
This article isn't even meant to explain why you ought to learn Haskell. It's more like a signpost on your path to mastery, should you begin walking it.
The Haskell community has a longstanding tradition of using condescending language ("fmap is from the street, fmap is hip to contexts."), and deliberate childrens-book style metaphors and illustrations in tutorials.
The theory seem to be that if monads haven't been adopted by mainstream developers yet, it is just because the presentations haven't been dumbed-down and kiddie-friendly enough yet. (If only they from the onset had called "monads" for "warm fuzzy things" instead, surely developers would not be so scared of them!)
The strategy have not yet borne fruit, though.
i wish people who are writing guides on these topics pick a non-simplified situation where using this method makes for an easier program (vs using the "traditional method"). The comparison and contrasting of a functional/monadic approach vs a procedural approach in a complex scenario might actually shed more light - at least, for some one who is familiar with the procedural approach.
http://book.realworldhaskell.org/read/programming-with-monad...
"Learn You A Haskell For Great Good" [1], while much less complete, is the best intro I have found so far. It's also free.
The audience level of this piece is confusing -- it looks like a friendly, cartoony introduction for a general audience, but it actually assumes you already know Haskell.
Basically, you and I are not the intended audience.