I think you can say that at the boundaries, applications aren't anything.
I tend to think of code in a cellular sense, as in, biology. Outside the cell is a big scary world that you don't control. There's a cell wall where you only permit certain things in. Inside the cell, the cell trusts that only good stuff has been let in. It may also have to package certain things on the way out to the next cell.
In this case, the observation I'd make is about that big scary external world. You don't get to impose anything on it, or at least, your control is a great deal less rigid than our code would like. Even if you think you control your internal network, hackers might explain otherwise to you in the worst possible way. You can't impose compliance with functional paradigms, imperative paradigms, security levels, soundness of data, whether or not a bit was flipped during transit, that the metadata matches what was sent, or anything.
Obviously you can't fully write your code that way (even real cells get it wrong sometimes too), but that's the principle I try to view the world through. Even within an application where every individual component is, say, compliant with functional programming, the interactions still can't be counted on to have any particular properties that you don't check somehow.
FP, OO, data-driven design, all that sort of stuff, that's for what you do inside the cells, and maybe how you choose to structure the code implementing your cell wall. But you almost always end up forced to treat the outside world as bereft of any structure you don't rigidly check for and enforce yourself, if not outright hostile (anything with security implications).
Yea, I think a lot of programmers confuse the map for the territory. It's not only the data, but the program itself.
Almost no one actually cares how a particular program was written or how it understands it's input and output -- we care that it works with some level of quality. How one gets that result is irrelevant in the end. It could be written directly in twisty assembly code. Do not care[1]
Parts of these paradigms have useful tools for building working programs, but a great majority of the contents of these paradigms are simply about organization. This shows up most clearly in OO, and of course, functions are a way to organize code. This isn't a bad thing -- certainly helpful for humans working on a code base -- but it isn't actually relevant to the task the program itself performs or how fast or well it performs it.
So, of course, the input and output of a program aren't really conformant to any paradigm, because the paradigms are about organizing programs, not about performing a particular task.
[1] (it might even be more reliable, in some cases, because you would be forced to be careful and pay attention and all those little details you want to ignore are right there in your face (see: async) :-))
I think you might miss the audience here...this is talking /to/ programmers, after all - who decidedly do care about how the program is written, organized, etc.
I don't think anyone is making a "more correct" or even "more performant" argument here; maybe, a "more reliable" argument - but only by extension of "better organized, so less likely to include certain classes of bugs".
> I think you can say that at the boundaries, applications aren't anything.
I think you very much can say that "at the boundaries, applications are procedural" (i.e., they do side-effecting things sequentially).
That's not incompatible with FP. On the contrary, FP used properly lets you push all that procedural code to smallish kernels at the "boundaries" so that all the rest of the code can be pure (thus easily tested).
> I think you very much can say that "at the boundaries, applications are procedural" (i.e., they do side-effecting things sequentially).
Well, side-effecting, yes, because that's literally how we define boundaries.
Sequentially? Not so much; concurrency (whether asynchrony or true parallelism) is important largely because simple sequential behavior doesn't capture what happens naturally at the boundaries well. (I suppose on an individual boundary, defined in the right way, there is likely to be a sequencing constraint, but not in aggregate across the boundaries of the system.)
You can parallelize as much as you want, but remember, you can't go faster than the slowest serial code. There will be some serial code. Again, I'm talking about order of steps in processing events that themselves may not arrive in any particular order.
"I think you very much can say that "at the boundaries, applications are procedural" (i.e., they do side-effecting things sequentially)."
You may be able to; I can't. I have a number of incoming event streams that are not necessarily ordered.
Now, like I said, you don't implement all code everywhere for all possible missteps, so you may have specific apps that get away with assuming orderedness. But it is not a general thing you can rely on.
> That doesn't make the application not-procedural. If it's having side effects, it's procedural in a sense.
“Procedural” is a structural paradigm; unstructured imperative code (old-school BASIC) has side effects but is not procedural in any sense (it is part of the broader category of imperative languages.) Also, “procedural” (or “imperative” or “functional”) is an attribute of programming languages, not applications/systems: Haskell is a pure functional programming languages, in which evaluating functions has no side effects, but it can define systems that have effects.
Perhaps I should have written "imperative" rather than "procedural", except no one really writes imperative non-procedural code now.
> Also, “procedural” (or “imperative” or “functional”) is an attribute of programming languages, not applications/systems:
It can be an attribute of programs regardless of language. It is possible to write functional-style code in C and procedural code in Haskell (just do everything in the IO monad!).
> Haskell is a pure functional programming languages, in which evaluating functions has no side effects, but it can define systems that have effects.
That's a bit of a fiction. Pure functions are pure, yes, but you can have impure functions -- Haskell is only interesting because you can have impure functions (otherwise every Haskell program would compile down into a constant), and what's really interesting about Haskell is the ideas that have evolved in its community about how to deal with impure functions.
> Pure functions are pure, yes, but you can have impure functions
Not in Haskell, you can't.
> Haskell is only interesting because you can have impure functions
No, it's interesting because it provides a way of representing series of effectful operations that are distinct from its functions, which are pure.
> otherwise every Haskell program would compile down into a constant
Every program in any language that is compiled compiles down to a constant (which is, itself, usually a program, often an imperative one in a native or virtual machine language); but in Haskell, each program is (in the model of the language, not merely what they compile to) normally a constant, non-function expression, most commonly of type IO ().
It's true that values of type IO a are isomorphic to “impure nullary functions returning a” in a language which has impure functions, but they aren't functions in Haskell, and can't be called from functions, they can only be operated on as values within the language.
Haskell's effectful operations are functions. Oh sure, not in the mathematical sense unless you model them as functions from World -> World.
> Every program in any language that is compiled compiles down to a constant ...
Sigh, yes, the compiled program is constant, but you know what I meant: a constant value, such as a number, that the program is expected to output. Let's not be this pedantic.
Things might be sequential at the boundaries or they might not. A lot of hardware interacting applications are forced to handle concurrent and out of order inputs that are expected to be processed in a particular order.
Really, since the boundary is where we push all the awful stuff - that boundary (depending on the application) can be any sort of terrible.
I tend to think of code in a cellular sense, as in, biology. Outside the cell is a big scary world that you don't control. There's a cell wall where you only permit certain things in. Inside the cell, the cell trusts that only good stuff has been let in. It may also have to package certain things on the way out to the next cell.
In this case, the observation I'd make is about that big scary external world. You don't get to impose anything on it, or at least, your control is a great deal less rigid than our code would like. Even if you think you control your internal network, hackers might explain otherwise to you in the worst possible way. You can't impose compliance with functional paradigms, imperative paradigms, security levels, soundness of data, whether or not a bit was flipped during transit, that the metadata matches what was sent, or anything.
Obviously you can't fully write your code that way (even real cells get it wrong sometimes too), but that's the principle I try to view the world through. Even within an application where every individual component is, say, compliant with functional programming, the interactions still can't be counted on to have any particular properties that you don't check somehow.
FP, OO, data-driven design, all that sort of stuff, that's for what you do inside the cells, and maybe how you choose to structure the code implementing your cell wall. But you almost always end up forced to treat the outside world as bereft of any structure you don't rigidly check for and enforce yourself, if not outright hostile (anything with security implications).