pasteldream

I’m not sure why witx’s comment was downvoted. This is absolutely the standard usage in math and computer science.

Yes. I’m not sure how slow it is in Julia, but pure functional languages do tend to generate more garbage for this reason. Hopefully the compiler can optimize it away in simple cases.

Edit: It’s not deepcopying the whole struct, just the parts that need to point to something new. So if you update a.b.c, it will shallow-copy a and a.b, but nothing else.

I think we’re talking past each other.

Lenses serve many purposes. All I’m saying is that in practice, the most common role they fulfil is to act as a counterpart for mutable references in contexts where you want or need immutability.

Can the use of lenses make a program more “composable”? Maybe, but if you have an example of a program taking advantage of that flexibility I’d like to see it.

Yeah, but I’m saying that in 90% of the cases where a functional program would use lenses, the corresponding imperative program would just use references.

> Your natural choice in the "OOP style" is to write a lot of boiler plate to point to each different field you want to get/set.

Your natural alternative to lenses in imperative languages is usually to just store a reference or pointer to the part you want to modify. Like a lens, but in-place.

Immutability gives you persistence, which can be practically useful. It’s not just fear.

Yeah, sorry, I realized after I commented.

But what’s the benefit of this approach? It seems needlessly expensive, both in terms of computational overhead (walking up and down the state tree) and how much more code it requires.

I guess you gain persistence of your entire app’s state (which makes time travel debugging easier) but that’s all I can think of.

You know, I do not actually know that a website had ads before clicking on a link to it; I would be happy to only visit websites without ads.

It’s scummy to shove ads in my face without at least warning me and giving me a chance to leave, I think.

Imagine asking the browser on my hardware to do things I don’t want it to do, and acting shocked when I tell it not to.

Can you point me to one of these reviews of case reports? As it is, your reply is too vague to be helpful.

How much do advertisers pay per customer, and where can I find this analysis?