[perrygeo]

> parse and interpret packet headers, apply validation rules, maintain BGP routing tables, add their own headers etc.

That's a few more than zero. I don't do network programming, that was just an example to show how even the quintessential IO-heavy application requires non-trivial calculations internally.

[whatnow37373]

Fair enough. It's just that in my experience the "cool bits" are quickly done and then we get bogged down in endless layers of inter-systems communication (HTTP, RPC, file systems, caches). I often see FP people saying stuff like "it's not 100% pure, of course there are some isolated side-effects" and I'm thinking.. my brother, I live inside side-effects. The days I can have even a few pure functions are few and far between. I'm honestly curious what percentage of your code bases can be this pure.

But of course this heavily depends on the domain you are working in. Some people work in simulation or physics or whatever and that's where the interesting bits begin. (Even then I'm thinking "programming" is not the interesting bit, it's the physics)

[BoiledCabbage]

> my brother, I live inside side-effects. The days I can have even a few pure functions are few and far between. I'm honestly curious what percentage of your code bases can be this pure.

I've never seen what you work on so there is no way I can say this with certainty, but generally people unfamiliar eith functional programming have way more code that is / or can be pure in their code base than they realize. Or put the opposite, directly as is if you were to go line by line in your code (skipping lines of comments and whitespace) and give every line a yes/no on whether is performs IO, what percentage are actually performing IO? Not are related to IO, or are preparing for or handing the results of IO, but how many lines are the actual line to write to the file or send the network packet?

Generally, it's a much smaller percentage than people are thinking because they are usually associating actual IO with things "related to" or "preparing for" or "handing results from" IO.

And then after finding that percentage to be lower than expected, it can also be made to be significantly lower by following a few functional programming design approaches.

[skydhash]

> The days I can have even a few pure functions are few and far between. I'm honestly curious what percentage of your code bases can be this pure.

A big part of it, I'm sure, but it requires some work. Pushing the side effects to the edge requires some abstractions to not directly mess with the original mutable state.

You are, in fact designing a state diagram from something that was evolving continuously on a single dimension: time. The transition of the state diagram are the code and the node are the inputs and output of that code. Then it became clear that IOs only matters when storing and loading those nodes. Because those nodes are finite and well defined, then the non-FP code for dealing with them became simpler to write.