[syklemil]

> Nope, pure functions are referentially transparent. The key idea is that you can replace the function invocation with a value and it shouldn’t change the program.

[Edit: This is wrong: And idempotent.] Generally you can expect that you can call them as many times as you like and get the exact same result. It _feels_ very safe.

> This isn't just a Haskell thing though. I'll write code this way in C# (and have built a large pure-FP framework for C# to facilitate this approach [1]).

I think that habit from Haskell is also what allowed me to pick up Rust pretty easily. You don't run afoul of the borrowchecker much if you don't expect to mutate a lot of stuff, and especially at a distance.

[chowells]

That's not what idempotent means. Idempotent means forall x, f(x)=f(f(x)). Most pure functions are not idempotent. Heck, f(f(x)) doesn't even type-check for most f. The typical name given to always getting the same results is just "pure". It doesn't depend on any implicit state anywhere.

[syklemil]

Right you are. I wish I had an excuse for my mistake, but I don't.