Why OCaml, why now? (2014)

- I like that with OCaml you can choose if you want your code to be functional or imperative, and both are equally well-supported. I am writing a compiler in OCaml, and I am able to use the API described in Peyton-Jones & Lester for doing pretty printing while still using imperative algorithms from the Dragon Book. This sometimes feels like cheating, but not having to figure out how to transform imperative code into functional code while still maintaining the same complexity constraints is really nice.

- OCaml code is usually a lot more "boring" than Haskell code, which is nice when reading other people's code. Let me explain: I am T.A.'ing an intro to compiler class where some students use Haskell and some use OCaml. The Haskell styles of the students varies a lot: some prefer to use point-free style, some used Parsec others AttoParsec, some passed state around manually while other use a state monad, etc. The OCaml submissions on the other hand were a lot more homogeneous: ocamllex for the scanner, menhir for the parser, the AST definition was almost identical to mine, and the code generation was also very similar.

- This may just be me, but I have had less problems with opam than with cabal. Also, the merlin tool and its integration with Emacs are really good and give me the kind of minimal, out-of-my-way IDE experience that I am looking for.

1. higher order functors.

2. modular type classes

Higher order functors are kind of cool, but IMO Standard ML does not seem to be suffering too much from the lack of them. I'm not too interested in it, since it gets super gnarly super fast, and this happens to be pretty much the main use-case for applicative functors. I suspect that most use-cases of higher order functors in OCaml could be reformulated to be first order, with a lot less monkeying around in the module system. There may be compelling use-cases though.

The other use-case is possibly a version of modular type classes that behaved a bit more like Haskell's. The idea is that if functors are going to be applied automatically during elaboration to provide something like type classes, you'll get MkWelp(S) called in multiple places, and you would prefer that any type members of the resulting structure be compatible. Applicative functors would do this.

I am not too convinced by this use-case, though I could see that people would find it useful.

In all other cases, generative functors have the correct semantics. Pretty much the whole use-case of putting abstract types in a functor is that you can then reason intensionally about them (i.e. distinguish them based on their access path). This is super useful, for instance, if you have a notion of "index" or something and you want to prevent yourself from using indexes from one table in another one, or something along those lines.

This is what the Scala people mystifyingly call "path dependent types". It's just generative abstraction.

So maybe it is an interesting feature to have applicative functors, but these should be added post facto, and generative functors should be the default. OCaml now supports generative functors if you add an extra () parameter; it's strange syntax, but it's good enough for me! :)

No, but hopefully it well help people who have yet to learn Haskell that not everyone thinks it's particularly difficult. I'm not interested in convincing the people who've tried and given up on it.

>That's great, but to people for whom they don't come so easily, this could easily be considered discouraging, or else bragging.

So what do you propose? That I pretend it's really hard for me, even though it's not? What effect do you think that's going to have?

>So unless you're SPJ or beyond, I wouldn't be quick to claim that Haskell isn't "unusually hard to learn."

You don't have to be SPJ to learn Haskell (or talk about how hard it is). Do I have to be Stroustrup to pass judgement on how hard it is to learn C++?

>In particular people who are older and have "work/life balance," ... and the life part of that work/life balance doesn't allow much time to do so.

I obviously don't mean that Haskell is easy for every single person in the world to learn; I mean that, as far as languages go, it's relatively easy enough to learn. If I didn't have enough time to learn Haskell, I also wouldn't have enough time to learn C++ or Python.

> but just maybe don't be so glib to claim it is not hard.

Again, what do you propose? Lie and tell people that it's super hard, so I don't hurt their feelings if they can't figure it out?