Hacker News Reader

Comment by kaba0 | Hacker News Reader

Here is a completely pure function in any imperative language:

  int add(int a, int b) {
    return a + b;
  }

View on HN

But the purity is implicit. Nothing will stop you from refactoring add into an impure function. As a programmer you have to maintain this mentally by remembering which types are pass by value and which are pass by reference.

Yes, this is a great example of a pillar of functional programming, pure functions. What is concerning is that your code example, like other pure function examples out there, implements a math operation a first grader can perform.

It's exceedingly difficult to find a pure functional example that operates on tangible domain-specific data of objects full of state.

It's not at all difficult (https://pandoc.org/). However, I'd hazard a guess that pandoc written in Rust or C (with idioms appropriate to those languages) would be much more performant.

I’m not as sure, several optimizations are only possible if we know that they can’t/won’t have side effects, and while the compiler can see it after inlining, having it part of the signature does help. Haskell is quite impressive on the performance front.

Reply on news.ycombinator.com