> Whenever I hear someone talking about purely functional programming, no side effects, I wonder what kind of programs they are writing
Where have you ever heard anyone talk about side-effect free programs, outside of academic exercises? The linked post certainly isn't about 100% side-effect/state free code.
Usually, people talk about minimizing side-effects as much as possible, but since we build programs to do something, sometimes connected to the real world, it's basically impossible to build a program that is both useful and 100% side-effect free, as you wouldn't be able to print anything to the screen, or communicate with other programs.
And minimizing side-effects (and minimizing state overall) have a real impact on how easy it is to reason about the program. Being really carefully about where you mutate things, leads to most of the code being very explicit about what it's doing, and code only affects data that is close to where the code itself is, compared to intertwined state mutation, where things everywhere in the codebase can affect state anywhere.
Where have you ever heard anyone talk about side-effect free programs, outside of academic exercises? The linked post certainly isn't about 100% side-effect/state free code.
Usually, people talk about minimizing side-effects as much as possible, but since we build programs to do something, sometimes connected to the real world, it's basically impossible to build a program that is both useful and 100% side-effect free, as you wouldn't be able to print anything to the screen, or communicate with other programs.
And minimizing side-effects (and minimizing state overall) have a real impact on how easy it is to reason about the program. Being really carefully about where you mutate things, leads to most of the code being very explicit about what it's doing, and code only affects data that is close to where the code itself is, compared to intertwined state mutation, where things everywhere in the codebase can affect state anywhere.