Comment by rumanator

> I think here lies the miscommunication, I'm talking about pure functions, it doesn't cease to be a function, but it does cease to be a pure one if sending its output somewhere else is done by side-effect.

No, you're getting it entirely wrong. The input is the translation unit, the output is the binaries. If you understand what a compiler does and what's it's role in a build process then you'll understand it works as a pure function. There are no side-effects. Translation units in, binaries out.

I suggest you spend some time with a tiny C or C++ project trying to arrive at an executable by performing all build steps by hand instead of using a Makefile or any form of high-level build system.