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Top Answer
Answered Jul 24, 2017 · 930 votes
If you want to get a feel for FRP, you could start with the old Fran tutorial from 1998, which has animated illustrations. For papers, start with Functional Reactive Animation and then follow up on links on the publications link on my home page and the FRP link on the Haskell wiki.
Personally, I like to think about what FRP means before addressing how it might be implemented. (Code without a specification is an answer without a question and thus "not even wrong".) So I don't describe FRP in representation/implementation terms as Thomas K does in another answer (graphs, nodes, edges, firing, execution, etc). There are many possible implementation styles, but no implementation says what FRP is.
I do resonate with Laurence G's simple description that FRP is about "datatypes that represent a value 'over time' ". Conventional imperative programming captures these dynamic values only indirectly, through state and mutations. The complete history (past, present, future) has no first class representation. Moreover, only discretely evolving values can be (indirectly) captured, since the imperative paradigm is temporally discrete. In contrast, FRP captures these evolving values directly and has no difficulty with continuously evolving values.
FRP is also unusual in that it is concurrent without running afoul of the theoretical & pragmatic rats' nest that plagues imperative concurrency. Semantically, FRP's concurrency is fine-grained, determinate, and continuous. (I'm talking about meaning, not implementation. An implementation may or may not involve concurrency or parallelism.) Semantic determinacy is very important for reasoning, both rigorous and informal. While concurrency adds enormous complexity to imperative programming (due to nondeterministic interleaving), it is effortless in FRP.
So, what is FRP? You could have invented it yourself. Start with these ideas:
- Dynamic/evolving values (i.e., values "over time") are first class values in themselves. You can define them and combine them, pass them into & out of functions. I called these things "behaviors".
- Behaviors are built up out of a few primitives, like constant (static) behaviors and time (like a clock), and then with sequential and parallel combination. n behaviors are combined by applying an n-ary function (on static values), "point-wise", i.e., continuously over time.
- To account for discrete phenomena, have another type (family) of "events", each of which has a stream (finite or infinite) of occurrences. Each occurrence has an associated time and value.
- To come up with the compositional vocabulary out of which all behaviors and events can be built, play with some examples. Keep deconstructing into pieces that are more general/simple.
- So that you know you're on solid ground, give the whole model a compositional foundation, using the technique of denotational semantics, which just means that (a) each type has a corresponding simple & precise mathematical type of "meanings", and (b) each primitive and operator has a simple & precise meaning as a function of the meanings of the constituents.Never, ever mix implementation considerations into your exploration process. If this description is gibberish to you, consult (a) Denotational design with type class morphisms, (b) Push-pull functional reactive programming (ignoring the implementation bits), and (c) the Denotational Semantics Haskell wikibooks page. Beware that denotational semantics has two parts, from its two founders Christopher Strachey and Dana Scott: the easier & more useful Strachey part and the harder and less useful (for software design) Scott part.
If you stick with these principles, I expect you'll get something more-or-less in the spirit of FRP.
Where did I get these principles? In software design, I always ask the same question: "what does it mean?". Denotational semantics gave me a precise framework for this question, and one that fits my aesthetics (unlike operational or axiomatic semantics, both of which leave me unsatisfied). So I asked myself what is behavior? I soon realized that the temporally discrete nature of imperative computation is an accommodation to a particular style of machine, rather than a natural description of behavior itself. The simplest precise description of behavior I can think of is simply "function of (continuous) time", so that's my model. Delightfully, this model handles continuous, deterministic concurrency with ease and grace.
It's been quite a challenge to implement this model correctly and efficiently, but that's another story.
Other Answers
Answered May 26, 2012 · 737 votes
In pure functional programming, there are no side-effects. For many types of software (for example, anything with user interaction) side-effects are necessary at some level.
One way to get side-effect like behavior while still retaining a functional style is to use functional reactive programming. This is the combination of functional programming, and reactive programming. (The Wikipedia article you linked to is about the latter.)
The basic idea behind reactive programming is that there are certain datatypes that represent a value "over time". Computations that involve these changing-over-time values will themselves have values that change over time.
For example, you could represent the mouse coordinates as a pair of integer-over-time values. Let's say we had something like (this is pseudo-code):
x = <mouse-x>;y = <mouse-y>;-
At any moment in time, x and y would have the coordinates of the mouse. Unlike non-reactive programming, we only need to make this assignment once, and the x and y variables will stay "up to date" automatically. This is why reactive programming and functional programming work so well together: reactive programming removes the need to mutate variables while still letting you do a lot of what you could accomplish with variable mutations.
If we then do some computations based on this the resulting values will also be values that change over time. For example:
minX = x - 16;minY = y - 16;maxX = x + 16;maxY = y + 16;-
In this example, minX will always be 16 less than the x coordinate of the mouse pointer. With reactive-aware libraries you could then say something like:
rectangle(minX, minY, maxX, maxY)-
And a 32x32 box will be drawn around the mouse pointer and will track it wherever it moves.
Here is a pretty good paper on functional reactive programming.
Other Answers
Answered Jun 23, 2009 · 144 votes
An easy way of reaching a first intuition about what it's like is to imagine your program is a spreadsheet and all of your variables are cells. If any of the cells in a spreadsheet change, any cells that refer to that cell change as well. It's just the same with FRP. Now imagine that some of the cells change on their own (or rather, are taken from the outside world): in a GUI situation, the position of the mouse would be a good example.
That necessarily misses out rather a lot. The metaphor breaks down pretty fast when you actually use a FRP system. For one, there are usually attempts to model discrete events as well (e.g. the mouse being clicked). I'm only putting this here to give you an idea what it's like.
1/5
Top Answer
Answered May 25, 2011 · 24 votes
R supports a mixture of object-oriented and functional programming paradigms.
On the functional side it:
- has first class functions
- has lazy evaluation of arguments
- encourages pure, side-effect free functions
But
- it does not implement tail call recursion
- and it's easy to create non-pure functions
On the object oriented side:
- it has three built in OO paradigms: S3 and S4, which are immutable and support generic function style OO, and reference classes (aka R5) which are mutable, and support the more common message-passing style OO.
- S4 is heavily influenced by the OO-style of common lisp (CLOS) and dylan.
- There are also a number of contributed packages that provide other types of OO: proto , mutatr , R.oo , OOP .
But
- The built-in OO tools provide little in the way of syntactic sugar.
2/5
Event-driven programming is a paradigm where the execution of a program is determined by events such as user actions or messages. Programs respond to events with predefined actions, allowing for asynchronous and responsive behavior, often seen in GUI applications and distributed systems.
Advantages of Event-Driven Programming Paradigm
- Enables asynchronous processing, optimizing resource utilization and responsiveness, crucial for real-time applications and user interfaces.
- Encourages modular code design, simplifying maintenance and scalability by separating concerns and promoting code reusability.
- Enhances user experience by responding promptly to user inputs, delivering a smoother and more interactive interface.
- Facilitates easier integration of new features or modifications, promoting adaptability to changing requirements in dynamic environments.
3/5
Top Answer
Answered Aug 06, 2019 · 186 votes
A functional language (ideally) allows you to write a mathematical function, i.e. a function that takes n arguments and returns a value. If the program is executed, this function is logically evaluated as needed.1
A procedural language, on the other hand, performs a series of sequential steps. (There's a way of transforming sequential logic into functional logic called continuation passing style.)
As a consequence, a purely functional program always yields the same value for an input, and the order of evaluation is not well-defined; which means that uncertain values like user input or random values are hard to model in purely functional languages.
1 As everything else in this answer, that’s a generalisation. This property, evaluating a computation when its result is needed rather than sequentially where it’s called, is known as “laziness”. Not all functional languages are actually universally lazy, nor is laziness restricted to functional programming. Rather, the description given here provides a “mental framework” to think about different programming styles that are not distinct and opposite categories but rather fluid ideas.
Other Answers
Answered May 26, 2012 · 737 votes
In pure functional programming, there are no side-effects. For many types of software (for example, anything with user interaction) side-effects are necessary at some level.
One way to get side-effect like behavior while still retaining a functional style is to use functional reactive programming. This is the combination of functional programming, and reactive programming. (The Wikipedia article you linked to is about the latter.)
The basic idea behind reactive programming is that there are certain datatypes that represent a value "over time". Computations that involve these changing-over-time values will themselves have values that change over time.
For example, you could represent the mouse coordinates as a pair of integer-over-time values. Let's say we had something like (this is pseudo-code):
x = <mouse-x>;y = <mouse-y>;-
At any moment in time, x and y would have the coordinates of the mouse. Unlike non-reactive programming, we only need to make this assignment once, and the x and y variables will stay "up to date" automatically. This is why reactive programming and functional programming work so well together: reactive programming removes the need to mutate variables while still letting you do a lot of what you could accomplish with variable mutations.
If we then do some computations based on this the resulting values will also be values that change over time. For example:
minX = x - 16;minY = y - 16;maxX = x + 16;maxY = y + 16;-
In this example, minX will always be 16 less than the x coordinate of the mouse pointer. With reactive-aware libraries you could then say something like:
rectangle(minX, minY, maxX, maxY)-
And a 32x32 box will be drawn around the mouse pointer and will track it wherever it moves.
Here is a pretty good paper on functional reactive programming.
Other Answers
Answered Jun 23, 2009 · 144 votes
An easy way of reaching a first intuition about what it's like is to imagine your program is a spreadsheet and all of your variables are cells. If any of the cells in a spreadsheet change, any cells that refer to that cell change as well. It's just the same with FRP. Now imagine that some of the cells change on their own (or rather, are taken from the outside world): in a GUI situation, the position of the mouse would be a good example.
That necessarily misses out rather a lot. The metaphor breaks down pretty fast when you actually use a FRP system. For one, there are usually attempts to model discrete events as well (e.g. the mouse being clicked). I'm only putting this here to give you an idea what it's like.
4/5
Top Answer
Answered Apr 12, 2018 · 7 votes
A non-functional declarative language is PROLOG. Programming in PROLOG is stating a number of facts, and then ask questions, which the system tries to verify or deny.
Example:
human(socrates). // "Socrates is a human."mortal(X) :- human(X). // "If X is a human, then X is mortal" or // "All humans are mortal."? mortal(socrates) // Is Socrates mortal?Yes.? mortal(X) // Who is mortal?socrates ? mortal(pythagoras). No. // since system doesn't know about any human except Socrates
Another well known language that is declarative, but not functional, is SQL.
Note that there are not only no functions as first class values. In the PROLOG example, there are no functions at all! To be sure, both SQL and PROLOG have some built-in functions, but have no way to let you write your own functions. One could think that the rule
mortal(X) :- human(X).-
is a function, but it isn't, it is an inference rule. Hence, declarative, non-functional languages.
For the second part of your question: it is certainly possible to write imperative code in functional programming languages. Simon Peyton Jones once stated that he thinks that Haskell is the finest imperative programming language in the world. (And this was only a half joke.)
Example:
main = do print "Enter a number" line <- getLine print (succ (read line :: Int))
5/5
www.geeksforgeeks.org › functional-programmingFunctional Programming Paradigm - GeeksforGeeks
www.geeksforgeeks.org › functional-programmingSep 2, 2024 · Functional programming is a programming paradigm in which we try to bind everything in pure mathematical functions. It is a declarative style. Its main focus is on “what to solve,” in contrast to an imperative style, where the main focus is on “how to solve.”
en.wikipedia.org › wiki › Functional_programmingFunctional programming - Wikipedia
en.wikipedia.org › wiki › Functional_programmingIn computer science, functional programming is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that map values to other values, rather than a sequence of imperative statements which update the running state ...
github.com › readme › guidesFunctional Programming 101 - GitHub
github.com › readme › guides“Functional programming [is] a paradigm that forces us to make the complex parts of our system explicit, and that’s an important guideline when writing software.” - José Valim, creator of Elixir. What are the rules of functional programming? There are two main things you need to know to understand the concept:
learntocodewith.me › learn › functional-programmingWhat Is Functional Programming? Benefits, Uses, & Languages
learntocodewith.me › learn › functional-programmingJul 7, 2023 · Functional programming paradigms are based on the concept of functions as the primary building blocks of programs. Functional programming focuses on creating pure functions that take inputs, process them, and return outputs without modifying the original data. It often also employs higher-order functions and recursion to solve problems.
www.freecodecamp.org › news › an-introduction-to-theAn Introduction to the basic principles of Functional Programming
www.freecodecamp.org › news › an-introduction-to-theNov 15, 2018 · What is functional programming? Functional programming is a programming paradigm — a style of building the structure and elements of computer programs — that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data — Wikipedia
www.educative.io › blog › what-is-functionalWhat is functional programming? Explained in Python, JS, and Java
www.educative.io › blog › what-is-functionalOct 15, 2020 · Functional programming is a declarative programming paradigm where programs are created by applying sequential functions rather than statements. Each function takes in an input value and returns a consistent output value without altering or being affected by the program state.
People also ask
What is functional programming?
- Functional programming is a programming paradigm in which we try to bind everything in pure mathematical functions style. It is a declarative type of programming style. Its main focus is on “what to solve” in contrast to an imperative style where the main focus is “how to solve”. It uses expressions instead of statements.
Functional Programming Paradigm - GeeksforGeeks
www.geeksforgeeks.org/functional-programming-paradigm/What is a functional programming paradigm?
- Functional programming paradigms are based on the concept of functions as the primary building blocks of programs. Functional programming focuses on creating pure functions that take inputs, process them, and return outputs without modifying the original data. It often also employs higher-order functions and recursion to solve problems.
What Is Functional Programming? Benefits, Uses, & Languages
learntocodewith.me/learn/functional-programming/What is functional programming in Python?
- Learn Functional Programming in Python What is functional programming? Functional programming is a declarative programming paradigm where programs are created by applying sequential functions rather than statements. Each function takes in an input value and returns a consistent output value without altering or being affected by the program state.
What is functional programming? Explained in Python, JS, and Java
www.educative.io/blog/what-is-functional-programming-python-js-javaWhat are some common uses of functional programming?
- Some common uses of functional programming are AI design, ML classification algorithms, financial programs, or advanced mathematical function models. Simplified: Functional programs execute many pure, single-purpose functions in sequence to solve complex mathematical or non-physical problems.
What is functional programming? Explained in Python, JS, and Java
www.educative.io/blog/what-is-functional-programming-python-js-javawww.infoworld.com › article › 2263963What is functional programming? A practical guide - InfoWorld
www.infoworld.com › article › 2263963Apr 1, 2021 · Functional programming means using functions to the best effect for creating clean and maintainable software. This article illustrates the concepts behind the functional...
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