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Comment by desumeku | Hacker News Reader

> it could build up a set internally, it could use a hashmap, or any one of a million other approaches. It can even probe the size of the array to pick the performance-optimal approach. I don't have to care.

Well, this is probably why functional programming doesn't see a lot of real use in production environments. Usually, you actually do have to care. Talk about noticing a performance regression because I was simply appending to an array. You have no idea what performance regressions are happening in ANY line of FP code, and on top of that, most FP languages are dead-set on "immutability" which simply means creating copies of objects wherever you possibly can... (instead of thinking about when it makes sense and how to be performant about it)

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Your assumption that filter/map/reduce is necessarily slower than a carefully handcrafted loop is wrong, though. Rust supports these features as well and the performance is equivalent.

Also countless real-world production environments run on Python, Ruby, JS etc, all of which are significantly slower than a compiled FP program using filter & map.

> FP languages are dead-set on "immutability" which simply means creating copies of objects

Incorrect. The compiler can make it mutable for better performance, and that gives you the best of both worlds: immutability where a fallible human is involved, and mutability where it matters.

> The compiler can make it mutable for better performance

Well, we already know that no pure FP language can match the performance of a dirty normal imperative language, except for Common Lisp (which I am happy to hear an explanation for how it manages to be much faster than the rest, maybe it's due to the for loops?). And another comment here already mentioned how those "significantly slower" scripting languages have a healthy dose of FP constructs -- which are normally considered anti-patterns, for good reason. The only language that competes in speed in Rust, which just so happens to let you have fast FP abstractions so long as you manually manage every piece of memory and its lifetime, constantly negotiating with the compiler in the process, thereby giving up any of the convenience benefits you actually get from FP.

You complain about not having control of how the `filter` works under the hood but are happy to give the language control over memory management. How much abstraction is too much abstraction? Where do you draw the line?

I consider an abstraction to be a good abstraction if I don't need to care for its internal workings all the time - whether that's some build step in the CI, or the usage of data structures from simple strings to advanced Cuckoo filters and beyond. Even Python uses a Bloom filter with operations on strings internally AFAIK. Correctness and maintainability trumps performance most of the time, and map, filter and immutability are building blocks to achieve just that. Those constructs won't prevent you from looking deeper and doing something different if you really have to (and know what you're doing), they just acknowledge that you'll probably don't need to do that.

> Correctness and maintainability trumps performance

Great, please make all the software even slower than it already is. I am overjoyed to have to purchase several new laptops a decade because they become e-waste purely due to the degradation of software performance. It is beyond ridiculous that to FP programmers daring to mutate variables or fine-tune a for loop is an exceptional scenario that you don't do "unless you have to" and which requires "knowing what you're doing". Do you know what you're doing? How can you be a software engineer and think that for loops are too difficult of a construct, and that you need something higher-level and more abstract to feel safe? It's insane. Utterly insane. Perhaps even the root of all evil, Code Golf manifested as religion.

> Great, please make all the software even slower than it already is.

It is more or less trivial to emit essentially optimal autovectorized and inlined machine code from functional iterators.

Rust does this, for example.

>Well, this is probably why functional programming doesn't see a lot of real use in production environments

The usual map/filter/reduce is everywhere in production. Python, java, js, ruby, c#...

You could even argue that lack of generics hurt Go's popularity for a while precisely for that usecase.

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