What is open recursion?

What is open recursion? | Not Hacker News!

Synthesized Answer

Based on 9 community responses

Open recursion is a concept in object-oriented programming where an object can call a method on itself, and that method can then call another method on the same object, potentially leading to recursive calls. This is made possible by the object's ability to refer to itself, often through a keyword like 'this' or 'self'. Open recursion allows for more flexibility in programming, as it enables objects to be extended or modified at runtime. However, it can also lead to complexity and potential issues if not managed carefully.

Key Takeaways

Open recursion involves an object calling methods on itself
It allows for flexibility and extensibility in object-oriented programming
It requires careful management to avoid complexity and potential issues

Discussion (9 comments)

Showing 9 comments

glhaynes

about 1 month ago

1 reply

This was really helpful and easy to follow. I came across this term the other day in that article that was going around about defining OOP and was a little baffled and thought "uh, I'll come back to this", but this gave me the perspective I needed to get it.

jerf

about 1 month ago

It's one of those things that's hard to get for most of us not because we don't understand what it is, but that we don't understand what not having it is like. Most languages in common use have this.

It can be similarly difficult to explain to people what structured programming is, because basically everything is structured programming now. The hard part is understanding what non-structured programming is, so that you can then understand the contrasts, because there is so little experience with it anymore.

chubot

about 1 month ago

2 replies

I wasn't really familiar with this term, but as another comment said here, the only language I use that doesn't have such late binding/dynamic dispatch is C

i.e. it seems natural in both Python and C++

But I did notice the term "open recursion" in Siek's Essentials of Compilation - https://mitpress.mit.edu/9780262048248/essentials-of-compila...

To make our interpreters extensible we need something called "open recursion", in which the tying of the recursive knot is delayed until the functions are composed. Objected-oriented languages provide open recursion via method overriding

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I mentioned that here too, on a thread about a type checker: https://news.ycombinator.com/item?id=45151620

To me the open recursion style clearly seems like a better default than VISITORS?

You can still REUSE traversal logic, and you don't "lose the stack", as I pointed out in the comment below: https://news.ycombinator.com/item?id=45160402

Am I missing something? I noticed there is a significant disagreement about style, which seems to not have a clear rationale: MyPy uses visitors all over, while TypeScript uses switch statements

This is a big difference! It affects nearly every line of code, and these projects have a ton of code ...

chubot

about 1 month ago

Also, I’m not 100% sure, but maybe Standard ML doesn’t support the open recursion pattern, but say OCaml does (?). So it could be a relevant distinction in that respect

1718627440

about 1 month ago

> the only language I use that doesn't have such late binding/dynamic dispatch is C

It's not that it doesn't support this, it is just explicit.

Akronymus

about 1 month ago

Am I understanding it correctly that those lambda functions are lexically bound rather than creating closures, in the "Open" section?

kazinator

about 1 month ago

[delayed]

agumonkey

about 1 month ago

Reminds me of tricks about implementing `letrec` in Lisp in small pieces.

skybrian

about 1 month ago

For an example of a language feature that looks kind of like standard object-oriented inheritance, but isn’t, check out “struct embedding” in Go. Struct embedding gives you the syntax of inheritance and you can even override methods, but for internal self-calls, methods don’t get overridden. (If you wanted to allow that, you’d need to add function pointers or an interface to the struct.)

View on Hacker NewsHN ID: 46121619Classification: qa

What is open recursion?

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