When haskell programmers say "functional" they mean "functions, like in math": yes, mathematics has higher-order functions (derivative, etc) but the main thing

When haskell programmers say "functional" they mean "functions, like in math": yes, mathematics has higher-order functions (derivative, etc) but the main thing is a mathematical function doesn't fire missiles or mutate variables (what we call "side-effects"). Writing code that's like math is "declarative"; you describe what things are not what to do. Others have given lots of good views on the various upsides to using haskell, especially the ways in which the type system can catch bugs for you. But my favorite thing about the type system is it lets you create good abstractions. For example it's possible (and often quite easy) to create a library which cannot be used incorrectly. And because you finally have abstractions which are good (not brittle or leaky) you can build on them to create larger abstractions (by "abstraction" here, think: conceptual unit that is easy to reason about). And that's also one of the challenges with learning haskell: there's more to learn because we can create new abstractions that are worth learning. I like talking about haskell, but certainly won't presume to tell you you should learn it. But if you want to learn and are put off by what you've seen of it on HN for whatever reason, I can tell you that the community is incredibly generous and full of very kind and smart folks (though some humility and an open mind, as always, will get you far). The community is why I actually have something of a career in software today.