> Every programming language is about side effects.
> Computations that don't lead to side effects are useless.
Right.
> The way one should visualize pure functional programming is that functional programs don't _do_ anything. They are equivalent to producing a description of the operation. The actual execution happens when those descriptions (generally encoded in effects or data types such as IO/Task) are interpreted by an external runtime.
This is the right way to understand imperative programming too. The program really doesn't do anything, it just describes a set of possible processes. Then the runtime converts the program into one of those processes (or maybe more than one). Each of those processes is a path through a program state space graph, but supposing your process is to have visual effects at various nodes in that graph the runtime will do externally visible things. It's really not any different.
In the end FP is basically just a way to force programming in a SSA style, plus whatever silliness the designers go for to deal with the reality that mathematical functions can't really capture input and output in any sort of useful way. Interestingly, it appears to me that in pure math the vernacular text around the equations fulfills that role.
> Computations that don't lead to side effects are useless.
Right.
> The way one should visualize pure functional programming is that functional programs don't _do_ anything. They are equivalent to producing a description of the operation. The actual execution happens when those descriptions (generally encoded in effects or data types such as IO/Task) are interpreted by an external runtime.
This is the right way to understand imperative programming too. The program really doesn't do anything, it just describes a set of possible processes. Then the runtime converts the program into one of those processes (or maybe more than one). Each of those processes is a path through a program state space graph, but supposing your process is to have visual effects at various nodes in that graph the runtime will do externally visible things. It's really not any different.
In the end FP is basically just a way to force programming in a SSA style, plus whatever silliness the designers go for to deal with the reality that mathematical functions can't really capture input and output in any sort of useful way. Interestingly, it appears to me that in pure math the vernacular text around the equations fulfills that role.