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Introduction 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. An expression is evaluated to produce a value whereas a statement is executed to assign variables. Those functions have some special features discussed below.
Functional Programming is based on Lambda Calculus: Lambda calculus is a framework developed by Alonzo Church to study computations with functions. It can be called as the smallest programming language in the world. It gives the definition of what is computable. Anything that can be computed by lambda calculus is computable. It is equivalent to Turing machine in its ability to compute. It provides a theoretical framework for describing functions and their evaluation. It forms the basis of almost all current functional programming languages. Fact: Alan Turing was a student of Alonzo Church who created Turing machine which laid the foundation of imperative programming style.
Programming Languages that...
- Pure functions
- Recursion
- Referential transparency
- Functions are First-Class and can be Higher-Order
- Variables are Immutable
- Pure functions are easier to understand because they don’t change any states and depend only on the input given to them. Whatever output they produce is the return value they give. Their function signature gives all the information about them i.e. their return type and their arguments.
- The ability of functional programming languages to treat functions as values and pass them to functions as parameters make the code more readable and easily understandable.
- Testing and debugging is easier. Since pure functions take only arguments and produce output, they don’t produce any changes don’t take input or produce some hidden output. They use immutable values, so it becomes easier to check some problems in programs written uses pure functions.
- It is used to implement concurrency/parallelism because pure functions don’t change variables or any other data outside of it.
- It adopts lazy evaluation which avoids repeated evaluation because the value is evaluated and stored only when it is needed.
- Sometimes writing pure functions can reduce the readability of code.
- Writing programs in recursive style instead of using loops can be bit intimidating.
- Writing pure functions are easy but combining them with the rest of the application and I/O operations is a difficult task.
- Immutable values and recursion can lead to decrease in performance.
- It is used in mathematical computations.
- It is needed where concurrency or parallelism is required.
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Introduction 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. An expression is evaluated to produce a value whereas a statement is executed to assign variables. Those functions have some special features discussed below.
Functional Programming is based on Lambda Calculus: Lambda calculus is a framework developed by Alonzo Church to study computations with functions. It can be called as the smallest programming language in the world. It gives the definition of what is computable. Anything that can be computed by lambda calculus is computable. It is equivalent to Turing machine in its ability to compute. It provides a theoretical framework for describing functions and their evaluation. It forms the basis of almost all current functional programming languages. Fact: Alan Turing was a student of Alonzo Church who created Turing machine which laid the foundation of imperative programming style.
Programming Languages...
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Top Answer
Answered Aug 23, 2008 · 94 votes
One key feature in a functional language is the concept of first-class functions. The idea is that you can pass functions as parameters to other functions and return them as values.
Functional programming involves writing code that does not change state. The primary reason for doing so is so that successive calls to a function will yield the same result. You can write functional code in any language that supports first-class functions, but there are some languages, like Haskell, which do not allow you to change state. In fact, you're not supposed to make any side effects (like printing out text) at all - which sounds like it could be completely useless.
Haskell instead employs a different approach to IO: monads. These are objects that contain the desired IO operation to be executed by your interpreter's toplevel. At any other level they are simply objects in the system.
What advantages does functional programming provide? Functional programming allows coding with fewer potentials for bugs because each component is completely isolated. Also, using recursion and first-class functions allows for simple proofs of correctness which typically mirror the structure of the code.
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Answered Jan 27, 2013 · 26 votes
What is functional programming
There are two different definitions of "functional programming" in common use today:
The older definition (originating from Lisp) is that functional programming is about programming using first-class functions, i.e. where functions are treated like any other value so you can pass functions as arguments to other functions and function can return functions among their return values. This culminates in the use of higher-order functions such as map and reduce (you may have heard of mapReduce as a single operation used heavily by Google and, unsurprisingly, it is a close relative!). The .NET types System.Func and System.Action make higher-order functions available in C#. Although currying is impractical in C#, functions that accept other functions as arguments are common, e.g. the Parallel.For function.
The younger definition (popularized by Haskell) is that functional programming is also about minimizing and controlling side effects including mutation, i.e. writing programs that solve problems by composing expressions. This is more commonly called "purely functional programming". This is made possible by wildly different approaches to data structures called "purely functional data structures". One problem is that translating traditional imperative algorithms to use purely functional data structures typically makes performance 10x worse. Haskell is the only surviving purely functional programming language but the concepts have crept into mainstream programming with libraries like Linq on .NET.
where would I want to use it instead of non-functional programming
Everywhere. Lambdas in C# have now demonstrated major benefits. C++11 has lambdas. There's no excuse not to use higher-order functions now. If you can use a language like F# you'll also benefit from type inference, automatic generalization, currying and partial application (as well as lots of other language features!).
am I correct in thinking that C is a non-functional programming language?
Yes. C is a procedural language. However, you can get some of the benefit of functional programming by using function pointers and void * in C.
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Answered Jun 20, 2020 · 6 votes
May be worth checking out this article on F# "101" on CoDe Mag recently posted.
Also, Dustin Campbell has a great blog where he has posted many articles on his adventures on getting up to speed with F#..
I hope you find these useful :)
EDIT:
Also, just to add, my understanding of functional programming is that everything is a function, or parameters to a function, rather than instances/stateful objects.. But I could be wrong F# is something I am dying to get in to but just dont have the time! :)
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Top Answer
Answered Jan 31, 2009 · 15 votes
If the programmer doesn't anticipate that [some input] could cause [program] to consume more-than-available resources, that's a vulnerability in the form of a possible DoS. This is a weakness of all Turing-complete languages I've seen, but Haskell's laziness makes it harder to reason about what a computation involves.
As a (rather contrived) example,
import Control.Monad (when)import System (getArgs)main = do files <- getArgs contents <- mapM readFile files flip mapM_ (zip files contents) $ \(file, content) -> when (null content) $ putStrLn $ file ++ " is empty"
The naïve programmer may think, "Haskell is lazy, so it won't open and read the files until it needs to", and "Haskell is garbage collected, so once it's done with a file, it can close the file handle". Unfortunately, this program actually will just open lots of files all at once (implementation-specific), and only the empty files will get their filehandles closed (side-effect of implementation's liveliness rules):
You might not be expecting a -EMFILE "Too many open files" error to ever occur.
Like I said, this is a contrived example, and can happen in other languages too, but it's just easier to miss certain resource usages in Haskell.
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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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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 ...
www.geeksforgeeks.org › functional-programmingFunctional Programming Paradigm - GeeksforGeeks
www.geeksforgeeks.org › functional-programmingJun 28, 2022 · Learn the basics of functional programming, a declarative style that uses pure mathematical functions. Explore its concepts, advantages, disadvantages and applications with examples and diagrams.
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 · Learn the basics of functional programming, such as pure functions, immutability, and higher order functions, with code examples in Clojure. Compare and contrast functional programming with object-oriented programming and see the benefits of functional programming.
People also ask
What is functional programming?
- This allows programs to be written in a declarative and composable style, where small functions are combined in a modular manner. Functional programming is sometimes treated as synonymous with purely functional programming, a subset of functional programming which treats all functions as deterministic mathematical functions, or pure functions.
Functional programming - Wikipedia
en.wikipedia.org/wiki/Functional_programmingWhat are the different programming paradigms?
- Different programming paradigms are based on different concepts, principles, and practices about the best way to code for different projects. Functional programming paradigms are based on the concept of functions as the primary building blocks of programs.
What Is Functional Programming? Benefits, Uses, & Languages
learntocodewith.me/learn/functional-programming/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-javagithub.com › readme › guidesFunctional Programming 101 · GitHub
github.com › readme › guidesFunctional programming is a paradigm that separates data and behavior, and uses pure functions that return new data or other functions. Learn the rules, benefits, and examples of functional programming, and how it differs from object-oriented programming.
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.
www.infoworld.com › article › 3613715What is functional programming? A practical guide | InfoWorld
www.infoworld.com › article › 3613715Apr 1, 2021 · Learn what functional programming is and how it differs from object-oriented and procedural programming. See how to use pure functions, immutability, first class functions, higher-order functions, and collections in JavaScript and Java.
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.
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