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Comment by danmaz74 | Hacker News Reader

Does anybody know of any language that supports OO, but that lets you declare pure functions/methods - enforcing that those pure functions/methods only use other pure functions, don't use global objects, etc? Lately we're adopting Redux [1] together with React and the idea of being able to mix functional and OO in a better way looks more and more interesting to me.

[1] https://github.com/rackt/redux

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Well, turns out that one of the oldest programming languages in existence, Fortran lets you do OOP, it also has pure functions and subroutines. I'm talking about about Fortran 95/2003/2008:

http://h21007.www2.hp.com/portal/download/files/unprot/fortr...

I would never have guessed. I wonder why this didn't spread more - it looks like a great way to mix FP and OOP.

I'm actually working on such a language [1]. It's OOP, but it makes a division between 'doing objects' (services) and 'being objects' (values). It's coming along, but it's still missing many vital things. It wasn't inspired by, but bares a striking resemblance to, the noop language [2].

[1] https://github.com/DanielWaterworth/plastic

[2] https://en.m.wikipedia.org/wiki/Noop

Good luck with your enterprise! My ideal would be to have this introduced to existing OOP languages (eg Ruby).

You can already write programs in this style in Ruby quite successfully, but there are advantages to having it baked into the language. It forces consistency and also opens up opportunities for tooling.

Unfortunately, I don't think it's something that can be bolted on after the fact.

Yes the checks were exactly what I was thinking about; that way you can be sure that you don't inadvertently do mistakes there. But probably Ruby (or javascript), with their ability of monkey patching, would make that almost impossible.

Maybe some Javascript "transpiler" could do it... it would be really interesting.

It's not just monkey patching that causes problems, though it certainly doesn't help.

The advantage of going with some sort of transpiler is that you can have two kinds of code within the same process whilst you make a gradual transition. I feel like, it could be made to work, but the boundary would have to be quite heavy-weight. Think less gradual typing and more FFI.

Edit: actually, in depends on which side is doing the calling. Going from checked to unchecked code is a minefield, but if it's unchecked code calling into checked code, it could work quite well as long as the arguments are immutable and don't have methods that can do IO.

Don't you need both in a language that supports both? I use a language that offers both but I only use methods.

C++....

I didn't work with C++ for 10 years now; is it now possible to declare a function "pure" and have checks that it doesn't have side effects?

It's called "const".

http://stackoverflow.com/questions/3141087/what-is-meant-wit...

That's interesting, but it's very far from making a pure function (ie, one that can't have side effects).

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