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1. Top results related to declarative programming vs imperative

   • Functional Programming Vs Declarative Programming Vs Imperative Programming

     Top Answer

     Answered Jan 26, 2021 · 130 votes

     Your example of declarative programming above is not an actual program, so it's not a good example.

     The main difference is between imperative and declarative. Functional is a particular kind of declarative.

     C, C++, Java, Javascript, BASIC, Python, Ruby, and most other programming languages are imperative. As a rule, if it has explicit loops (for, while, repeat) that change variables with explicit assignment operations at each loop, then it's imperative.

     SQL and XSLT are two well-known examples of declarative programming. Markup languages such as HTML and CSS are declarative too, although they are usually not powerful enough to describe arbitrary algorithms.

     Here is an example computation (summing the income by gender, from a suitable data source) first written in an imperative language (Javascript) and then in a declarative language (SQL).

     Imperative programming

     var income_m = 0, income_f = 0;for (var i = 0; i < income_list.length; i++) { if (income_list[i].gender == 'M') income_m += income_list[i].income; else income_f += income_list[i].income;}-

     Notice:

     • explicit initialization of variables that will contain the running totals;
     • explicit loop over the data, modifying the control variable ( i) and the running totals at each iteration;
     • conditionals ( ifs) are only used to choose the code path at each iteration.

     Declarative programming

     select gender, sum(income)from income_listgroup by gender;-

     Notice:

     • memory cells to contain running totals are implied by the output you declare you want;
     • any loop the CPU will need to perform (eg. over the income_list table) is implied by the output you declare you want and by the structure of the source data;
     • conditionals (eg. case in SQL) are used in a functional way to specify the output value you want based on the input values, not to choose a code path.

     Functional programming

     As I mentioned above, SQL's case is a great example of the functional way of programming, which is a restricted subset of Declarative programming in which the desired computation is specified by composing functions.

     Functions are things that accept inputs and return outputs (eg. case, sum()…)

     Composition means chaining two or more together by specifying how the output of one is fed as the input to the next (typically by writing one inside the other.) Finally the whole composition, which is still itself a big function, is applied to the available inputs to get the desired output.

     In this snippet I am declaring the output I want by composing the functions sum() and case. This is called functional programming:

     select sum(case when some_flag = 'X' then some_column else some_other_column end)from ...-

     If the composition of two or more functions and their application to the input data are the only constructs available in a given language, that language is said to be purely functional. In those languages you will notice the complete absence of loops, variable assignment and other typically imperative statements.

     Edit: I recommend watching some of Anjana Vakil's talks on functional programming in Javascript, to get a better idea of what it's about.

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   • Incrementing a counter with functional programming vs imperative programming

     Top Answer

     Answered Mar 30, 2022 · 2 votes

     This question seems to originate from the misunderstanding that there's no state in Functional Programming (FP). While this notion is understandable, it's not true.

     In short, FP is an approach to programming that makes an explicit distinction between pure functions and everything else (often called impure actions). Simon Peyton-Jones (SPJ, one of the core Haskell developers) once gave a lecture where he said something to the effect that if you couldn't have any side effects, the only thing you could do with a pure function would be to heat the CPU, whereafter one student remarked that that would also be a side effect. (It's difficult to find the exact source of this story. I recall having seen an interview with SPJ where he related the story, but searching the web for a quote in a video is still hard in 2022.)

     • Changing a pixel on the screen is a side effect.
     • Sending an email is a side effect.
     • Deleting a file is a side effect.
     • Creating a row in a database is a side effect.
     • Changing an internal variable that, via cascading consequences, causes anything like the above to happen, is a side effect.

     It is impossible to write (useful) software that has no side effects.

     Furthermore, pure functions also don't allow non-deterministic behaviour. That excludes even more necessary actions:

     • Getting a (truly) random number is non-deterministic.
     • Getting the time or date is non-deterministic.
     • Reading a file is non-deterministic.
     • Querying a database is non-deterministic.
     • Etc.

     FP acknowledges that all such impure actions need to take place. The difference in philosophy is the emphasis on pure functions. A pure function has many desirable traits (predictability, referential transparency, possible memoization, testability) that makes it worthwhile to pursue a programming philosophy that favours such functions.

     A functional architecture is one that minimises the impure actions to their essentials. One label for that is Functional Core, Imperative Shell, where you push all impure actions to the edge of your system. That would, for example, include an HTML counter. Actually changing an HTML element stays imperative, while the calculation required to produce the new value can be implemented as a pure function.

     Different languages have varying approaches to how explicitly they model the distinction between pure functions and impure actions. Most languages (even 'functional' languages like F# and Clojure) don't explicitly make that distinction, so it's up to the programmer to keep that separation in mind.

     Haskell is one language that famously does make that distinction. It uses the IO monad to explicitly model impure actions. I've attempted to explain IO for object-oriented programmers using C# as an example language in an article: The IO Container.

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   • Imperative and declarative steps in Rspec

     Top Answer

     Answered Aug 19, 2010 · 8 votes

     Declarative is the way forward.

     Imperative describes the actual UI steps you have to take as a user, rather than the results you're trying to achieve. If you write your scenarios this way they'll become really brittle and impossible to maintain. Imagine if someone put a confirmation box in that imperative scenario, and there were 80 similar scenarios which also required changing.

     With declarative steps you only need to change it in the one place where the step is defined; that same declarative step is then reused for all the scenarios which need it.

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     3/5

   • Imperative vs Functional - understanding the von Neumann bottleneck

     Top Answer

     Answered Apr 16, 2018 · 1 votes

     You need to read the original paper published by John Backs "Can Programming Be liberated from the Von Neumann Style? A functional style and its algebra of programs". It basically talks about two kinds of bottlenecks one which is physical hardware limitations and the other which is a kind of conceptual bottleneck formed due to the way programmers think of languages. On your second question. As earlier languages were more closer to the respective hardware implementations the programmer thinking used to be mimic the sequential flow of events. Functional languages give us a new way to look at programs wherein parallel executions or operations on a set of data work.

     On the first question I would like to iterate a comment from wiki.c2.com

     "What does the choice of programming language have on the hardware? A functional language which is compiled to run on a von Neumann machine will still suffer the bottleneck." The answer, is ReferentialTransparency--which makes parallel computation much more tractable (and capable of being automated). Effectively parallelizing imperative languages is still an active research topic.

     http://wiki.c2.com/?CanProgrammingBeLiberatedFromTheVonNeumannStyle

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   • Declarative programming in java

     Top Answer

     Answered Apr 22, 2012 · 6 votes

     As a commenter said, your example is more functional programming than declarative programming, although the two are similar in some respects. In real declarative programming, you'd be more results oriented -- you'd be specifying what to do with the interesting elements in the list, rather than transforming the list for its own sake. A rule engine like Jess is an example of a declarative programming system (disclaimer, I'm the author of Jess.)

     To answer your one simple question: yes. All functional or declarative programming systems involve a runtime system that has to be implemented on the real computer the program is running on. Since the real computer is invariably an imperative von Neumann machine, that runtime system has to be written imperatively. It is therefore an additional layer of abstraction between your program and the hardware.

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2. www.educative.io › blog › declarative-vs-imperativeDeclarative vs imperative programming: 5 key differences

   www.educative.io › blog › declarative-vs-imperative

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   Learn the concepts and examples of declarative and imperative programming paradigms, and how they differ in terms of control flow, expressiveness, and readability. Find out which languages support both paradigms and how to get started with declarative programming today.

3. www.freecodecamp.org › news › imperative-vsImperative vs Declarative Programming – the Difference ...

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   Oct 8, 2020 · Learn the difference between imperative and declarative programming styles and how to use them in JavaScript. Imperative programming gives step by step instructions, while declarative programming defines what things are.

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4. stackoverflow.com › questions › 1784664What is the difference between declarative and imperative ...

   stackoverflow.com › questions › 1784664

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   Imperative programming tells the machine how to do something (resulting in what you want to happen) Declarative programming tells the machine what you would like to happen (and the computer figures out how to do it) Two examples: 1. Doubling all numbers in an array. Imperatively:

   Usage example

   Declarative <<=====|==================>> Imperative

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5. www.geeksforgeeks.org › difference-betweenDifference Between Imperative and Declarative Programming

   www.geeksforgeeks.org › difference-between

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   Mar 22, 2023 · Learn the difference between imperative and declarative programming paradigms, their examples, advantages and disadvantages. Imperative programming focuses on how to get the answer step by step, while declarative programming focuses on what to get the answer.

   Imperative Programming	Declarative Programming
   In this, programs specify how it is to be ...	In this, programs specify what is to be ...
   It simply describes the control flow of ...	It simply expresses the logic of ...
   Its main goal is to describe how to get ...	Its main goal is to describe the desired ...
   Its advantages include ease to learn and ...	Its advantages include effective code, ...

   See full list on geeksforgeeks.org

6. People also ask

   What is declarative programming?

   • In contrast with imperative programming, declarative programming describes what you want the program to achieve rather than how it should run. In other words, within the declarative paradigm, you define the results you want a program to accomplish without describing its control flow.

   Declarative vs imperative programming: 5 key differences - Educative

   www.educative.io/blog/declarative-vs-imperative-programming

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   What is imperative programming?

   • Imperative programming is the oldest and most basic programming approach. Within the imperative paradigm, code describes a step-by-step process for a program’s execution. Because of this, beginners often find it easier to reason with imperative code by following along with the steps in the process.

   Declarative vs imperative programming: 5 key differences - Educative

   www.educative.io/blog/declarative-vs-imperative-programming

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   What is the difference between imperative and declarative programming?

   • In declarative programming, the system optimizes the code based on the rules and constraints specified by the programmer. In imperative programming, variables can be mutable. In declarative programming, variables are typically immutable. Summer-time is here and so is the time to skill-up!

   Difference Between Imperative and Declarative Programming

   www.geeksforgeeks.org/difference-between-imperative-and-declarative-programming/

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   What happens when you switch from imperative to declarative programming?

   • A major shift in thinking occurs when we switch from imperative to declarative programming. Once my students have learned basic JavaScript, we go over functional programming and the array methods used in a declarative coding style. This is where their brains start to pop and sizzle and melt like marshmallows over a fire.

   Imperative vs Declarative Programming – the Difference Explained in

   www.freecodecamp.org/news/imperative-vs-declarative-programming-difference/

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7. codefresh.io › learn › infrastructure-as-codeDeclarative vs. Imperative Programming: 4 Key Differences

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   • Syntax and Code Structure. Declarative programming languages generally have a high-level, expressive syntax that allows you to describe what you want to achieve in a clear, concise manner.
   • Abstraction Level. Another significant difference is the level of abstraction. Declarative programming languages are usually higher-level, meaning they abstract away many of the details associated with how the program executes.
   • State Management. In declarative programming, state is typically managed automatically by the language or framework. You describe the desired state of the system, and the underlying implementation takes care of maintaining it.
   • Control Flow. Control flow refers to the order in which the instructions in a program are executed. In declarative programming, control flow is typically implicit and determined by the language or framework.

8. www.baeldung.com › cs › imperative-vs-declarativeImperative and Declarative Programming Paradigms - Baeldung

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   Mar 18, 2024 · Learn the differences and similarities between imperative and declarative programming paradigms and their derived paradigms of procedural, object-oriented, functional, and logic programming. See examples of languages and concepts for each paradigm.

9. ui.dev › imperative-vs-declarative-programmingImperative vs Declarative Programming

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   Learn the difference between imperative and declarative programming with metaphors and code examples. Imperative programming is how you do something, declarative programming is more like what you do.