7 ms·

So you would call: arr .map(x => x + 2) .filter(x => x % 3) .map(x => other(x)) Imperative?

by Trufa 6y ago

nevir 6y ago
Yes. That is imperative. Declarative code describes the _output_ or final desired state of something.
- hyperpallium 6y ago
  Is f(g(x)) imperative? There's an ordering... and it works in terms of mappings, not outputs...
  - lhorie 6y ago
    Depends on what language you're using. In math notation, given `y = x * x`, you can work backwards from `y = 4` to figure out the value of x, whereas in, say, Javascript, `y = x * x` means exactly "compute y as the value of x times itself" and only that. For illustration, we could also compute the square of x in a different imperative form, e.g. in terms of a loop over additions. Similarly, in mathematical notation, `f(g(x))` can be a way of expressing the existence of some sort of law, e.g. maybe f and g are commutative. That means that if code were written as such in a 5th-gen language[1], the underlying engine is free to recompile the code into `g(f(x))` assuming the commutative property holds and the performance is better. By contrast, in a imperative language, `f(g(x))` generally would compile to that exact order of operations (unless you have a mythical sufficiently smart compiler) I can see an argument about JIT compilers being smart in some cases, but the philosophical distinction between imperative and declarative paradigms is that with declarative style, the compiler can transparently swap units of arbitrary complexity. For example, given some CSS rules, a browser engine can decide to paint the screen buffer however it wants, be it top-to-bottom, edge-to-center, layer-over-layer, etc regardless of how the CSS was originally expressed. [1] https://en.wikipedia.org/wiki/Fifth-generation_programming_language https://en.wikipedia.org/wiki/Fifth-generation_programming_l...
    - hyperpallium 6y ago
      I meant in math. BTW, pedantry: -2 * -2 = 4 too
- barrkel 6y ago
  It's not so simple. Compiled programming languages are declarative ways of generating machine code. The source code describes what the output or final state (the executable) should consist of, but not how to construct it (that's in the compiler source). Is the code "read x; print x + 5" declarative or imperative? It's declarative because it doesn't specify how to read the number, how to print the result, or how to add numbers. It merely symbolically describes the IO and calculations to be performed. It's imperative because it specifies in a step-wise fashion reading input, performing a calculation, and outputting the result. Declarative code is imperative from the perspective of the next layer up in the abstraction stack. Declarative code elides implementation details; the we call the implementation details imperative, because they specify the "how" and not the "what", which is the domain of the higher level. Under this lens, what can we say about this: arr .map(x => x + 2) .filter(x => x % 3) .map(x => other(x)) It's imperative if we understand map() and filter() to be imperative operations. If they're declarative - perfectly possible in C# - then the code is declarative, because `arr` could be quite abstract, and do something much more interesting.
deleted 6y ago
[deleted]
cool-RR 6y ago
The border is fuzzy, so there wouldn't be a yes or no answer. Here are a couple of things that make your example more declarative than OP's code: 1. While each line is a separate step that's done in order, it's done on the results of the previous step. So it's like "get me the sum of the products of the results of foo" rather than "do x, then do y, then do z". 2. Your example has less steps.
lbarrow 6y ago
Compared with SQL it's definitely imperative. It's definitely using higher-level abstractions than a `for` loop, but it still specifies the order of operations.
- nicoburns 6y ago
  > it still specifies the order of operations Yes, although not necessarily all of them. Some languages will process this eagerly, some lazily.
- deleted 6y ago
  [deleted]
- barrkel 6y ago
  Actually it doesn't unless you're assuming eager evaluation and that 'arr' is something like an array, rather than something which monadically collects functions for evaluation later. In C#, the functions being passed could be passed as analyzable syntax trees, and the implementation could actually be in SQL.
- sriram_malhar 6y ago
  nope. Sequencing and imperative have an overlap, but they are not the same thing. Sequencing is a fundamental computing construct. Data flow graphs allow you to specify sequences, just as shell pipelines do. SQL has sequentiality built-in with nested queries. None of these are imperative environments.
TimTheTinker 6y ago
Yes and no. It’s a functional chain of higher-order operations over a collection. So yes—-it is imperative, but it uses functional abstraction to reduce complexity.
darksaints 6y ago
I would. Because at the pure end imperative->declarative spectrum, you lose turing completeness. It is certainly less imperative than the equivalent C, that's for sure.
- hexane360 6y ago
  That's not true at all. The following is a declarative program: Yield an interpretation of a set of boolean variables that satisfies the following conditions: - A AND B - (NOT C) or A or B - A AND (NOT C) ...etc
  - deleted 6y ago
    [deleted]

So you would call: arr .map(x => x + 2) .filter(x => x % 3) .map(x => other(x)) Imperative?

by Trufa 6y ago

So you would call: arr .map(x => x + 2) .filter(x => x % 3) .map(x => other(x)) Imperative?

nevir 6y ago

Yes. That is imperative. Declarative code describes the _output_ or final desired state of something.

hyperpallium 6y ago
Is f(g(x)) imperative? There's an ordering... and it works in terms of mappings, not outputs...
- lhorie 6y ago
  Depends on what language you're using. In math notation, given `y = x * x`, you can work backwards from `y = 4` to figure out the value of x, whereas in, say, Javascript, `y = x * x` means exactly "compute y as the value of x times itself" and only that. For illustration, we could also compute the square of x in a different imperative form, e.g. in terms of a loop over additions. Similarly, in mathematical notation, `f(g(x))` can be a way of expressing the existence of some sort of law, e.g. maybe f and g are commutative. That means that if code were written as such in a 5th-gen language[1], the underlying engine is free to recompile the code into `g(f(x))` assuming the commutative property holds and the performance is better. By contrast, in a imperative language, `f(g(x))` generally would compile to that exact order of operations (unless you have a mythical sufficiently smart compiler) I can see an argument about JIT compilers being smart in some cases, but the philosophical distinction between imperative and declarative paradigms is that with declarative style, the compiler can transparently swap units of arbitrary complexity. For example, given some CSS rules, a browser engine can decide to paint the screen buffer however it wants, be it top-to-bottom, edge-to-center, layer-over-layer, etc regardless of how the CSS was originally expressed. [1] https://en.wikipedia.org/wiki/Fifth-generation_programming_language https://en.wikipedia.org/wiki/Fifth-generation_programming_l...
  - hyperpallium 6y ago
    I meant in math. BTW, pedantry: -2 * -2 = 4 too
barrkel 6y ago
It's not so simple. Compiled programming languages are declarative ways of generating machine code. The source code describes what the output or final state (the executable) should consist of, but not how to construct it (that's in the compiler source). Is the code "read x; print x + 5" declarative or imperative? It's declarative because it doesn't specify how to read the number, how to print the result, or how to add numbers. It merely symbolically describes the IO and calculations to be performed. It's imperative because it specifies in a step-wise fashion reading input, performing a calculation, and outputting the result. Declarative code is imperative from the perspective of the next layer up in the abstraction stack. Declarative code elides implementation details; the we call the implementation details imperative, because they specify the "how" and not the "what", which is the domain of the higher level. Under this lens, what can we say about this: arr .map(x => x + 2) .filter(x => x % 3) .map(x => other(x)) It's imperative if we understand map() and filter() to be imperative operations. If they're declarative - perfectly possible in C# - then the code is declarative, because `arr` could be quite abstract, and do something much more interesting.

deleted 6y ago

[deleted]

cool-RR 6y ago

The border is fuzzy, so there wouldn't be a yes or no answer. Here are a couple of things that make your example more declarative than OP's code: 1. While each line is a separate step that's done in order, it's done on the results of the previous step. So it's like "get me the sum of the products of the results of foo" rather than "do x, then do y, then do z". 2. Your example has less steps.

lbarrow 6y ago

Compared with SQL it's definitely imperative. It's definitely using higher-level abstractions than a `for` loop, but it still specifies the order of operations.

nicoburns 6y ago
> it still specifies the order of operations Yes, although not necessarily all of them. Some languages will process this eagerly, some lazily.
deleted 6y ago
[deleted]
barrkel 6y ago
Actually it doesn't unless you're assuming eager evaluation and that 'arr' is something like an array, rather than something which monadically collects functions for evaluation later. In C#, the functions being passed could be passed as analyzable syntax trees, and the implementation could actually be in SQL.
sriram_malhar 6y ago
nope. Sequencing and imperative have an overlap, but they are not the same thing. Sequencing is a fundamental computing construct. Data flow graphs allow you to specify sequences, just as shell pipelines do. SQL has sequentiality built-in with nested queries. None of these are imperative environments.

TimTheTinker 6y ago

Yes and no. It’s a functional chain of higher-order operations over a collection. So yes—-it is imperative, but it uses functional abstraction to reduce complexity.

darksaints 6y ago

I would. Because at the pure end imperative->declarative spectrum, you lose turing completeness. It is certainly less imperative than the equivalent C, that's for sure.

hexane360 6y ago
That's not true at all. The following is a declarative program: Yield an interpretation of a set of boolean variables that satisfies the following conditions: - A AND B - (NOT C) or A or B - A AND (NOT C) ...etc
- deleted 6y ago
  [deleted]