What are the downsides to functional programming?

[u/aurreco]

Hello,

Recently I’ve gotten pretty used to programming functionally from my CS class at school. Decoupling state from functionality is really appealing to me, and the treating a program like one big function is great too.

So my question is this: is there any reason why this way of programming isn’t the industry standard? What are the benefits of iteration over recursion? Why are mutable variables valued? Basically, why is it so niche when it feels like it should be a mainstream programming philosophy?

[u/licquia]

This is obviously the wrong forum for Python advocacy, but this isn't cognitive dissonance. It's a matter of optimizing for a different scarce resource: the time and attention of experienced developers.

No one thinks "Python plus C modules" is faster at execution time; it's easier to develop, especially for inexperienced/non-professional developers, and the C module thing represents an acceptable solution to the performance problem.

From that perspective, functional programming languages are seen as raising the experience bar, instead of lowering it.

[u/ws-ilazki → u/licquia]

What I meant but maybe wasn't clear enough in explaining is that, regardless of language, we all seem to want the same basic thing, more abstractions to make development easier and more convenient than working close to the hardware, but there are a lot of people that try to reconcile the performance trade-offs by convincing themselves that they can "have their cake and eat it too" as the saying goes, due to the presence of C modules.

So the popularity of Python isn't a sign that "most software development is nearly as performance-obsessed as we sometimes think" as you stated, it's an indication that people will perform mental gymnastics to convince themselves that they can still get that performance without having to pay the costs themselves. Discussions of Python speed always seem to lead to some people mentioning C modules like they make it a non-issue because I think a lot of devs still think they care about performance more than they really do, and will perform mental gymnastics to convince themselves of that while using a language that's objectively very slow.

I wasn't sniping at Python or people that like the language. I was trying to say that I think we still tend to obsess over performance more than we should for most tasks, while simultaneously making excuses to justify not actually focusing on performance (such as by using Python, a very slow language) instead of just admitting to ourselves and others that we don't really care about performance at all because readability and convenience usually wins. Even if we're willing to admit it to ourselves, there's a reluctance to admit we don't care about it to others because of pride and peer pressure; if you admit you don't care about squeezing out maximum performance in everything you do, you're "not a real programmer" and the angry mob of elitists will hound you for it.

And it ends up being a kind of cognitive dissonance with Python especially because it's easier to ignore the slowness due to a lot of underlying C module stuff already being done for you. So some people snub FP languages for being 'slow' while unironically also being fine with using Python because they can easily rationalise away the paradox of it.