4 ms·

How do you “Hello World” in a functional language? Doesn’t it have side effects?

sevensor 2y ago
There's some real confusion about what "functional" means, because it depends on who's speaking. Writing _exclusively_ pure functions is a Haskell thing. A much looser definition of the functional style would be to say that you mostly write pure functions over immutable data, but when you have to actually do a side effect you write a procedure that talks to the outside world and go on with your day. If you go digging in this site's archives from about ten years ago, I recall numerous debates about what constituted functional programming, and whether the latter counts at all. But if we _are_ talking about Haskell, the answer to your question is obviously "Monads."
cess11 2y ago
The string "Hello World" evaluates to itself, what else do you need? Edit: Eh, I thought it was a fun quip.
- pyuser583 2y ago
  I laughed
- NateEag 2y ago
  Never forget PHP's "Hello World": Hello, world!
trealira 2y ago
Yes, and AFAIK, you're pretty much free to cause side-effects in functional languages; it's just a bit awkward and somewhat discouraged. It's kind of like how C still has goto, yet it's still a structured programming language. Even in Haskell, which tries to control side-effects more, it's not hard; it's just that it's stuck with an "IO" annotation. Any function that calls an IO function also becomes an IO function; it's infectious. main :: IO () main = putStrLn "hello, world"
dllthomas 2y ago
It has an effect. Whether it's a "side effect" depends on how we've defined that. One way of viewing Haskell is that you are lazily constructing the single composite "effect on the world" called main. helloWorld :: IO () then is a value representing an effect, but it only actually happens when it becomes a part of main. Threads complicate this but don't completely destroy the model.

There's some real confusion about what "functional" means, because it depends on who's speaking. Writing _exclusively_ pure functions is a Haskell thing. A much looser definition of the functional style would be to say that you mostly write pure functions over immutable data, but when you have to actually do a side effect you write a procedure that talks to the outside world and go on with your day. If you go digging in this site's archives from about ten years ago, I recall numerous debates about what constituted functional programming, and whether the latter counts at all. But if we _are_ talking about Haskell, the answer to your question is obviously "Monads."

cess11 2y ago

The string "Hello World" evaluates to itself, what else do you need? Edit: Eh, I thought it was a fun quip.

pyuser583 2y ago
I laughed
NateEag 2y ago
Never forget PHP's "Hello World": Hello, world!

trealira 2y ago

Yes, and AFAIK, you're pretty much free to cause side-effects in functional languages; it's just a bit awkward and somewhat discouraged. It's kind of like how C still has goto, yet it's still a structured programming language. Even in Haskell, which tries to control side-effects more, it's not hard; it's just that it's stuck with an "IO" annotation. Any function that calls an IO function also becomes an IO function; it's infectious. main :: IO () main = putStrLn "hello, world"

dllthomas 2y ago

It has an effect. Whether it's a "side effect" depends on how we've defined that. One way of viewing Haskell is that you are lazily constructing the single composite "effect on the world" called main. helloWorld :: IO () then is a value representing an effect, but it only actually happens when it becomes a part of main. Threads complicate this but don't completely destroy the model.