F# gives yousimplicity like Python withcorrectness,robustness andperformance beyond C# or Java.
F# isopen source,cross-platform andfree to use withprofessional tooling.
F# is aJavaScript and.NET language forweb,cloud,data-science,apps and more.
HelloWorld.fslethelloname=printfn$"Hello, {name}!"letgreets=["World""Solar System""Galaxy""Universe""Omniverse"]greets|>List.iterhelloConcise like Python
F#’s elegant syntax and strong typing give you the tools to solve problems succinctly, robustly and happily.
Concise like Python
F#’s elegant syntax and strong typing give you the tools to solve problems succinctly, robustly and happily.
- Concise syntax defines reusable functions with minimal boilerplate
- Simple lists uses indentation-based syntax without requiring commas
- String interpolation provides readable string formatting with the
$prefix - Pipeline operator creates a readable left-to-right flow of data
In just a few lines of code, F# provides a clean, readable implementation that would require significantly more boilerplate in many other languages. This expressive style becomes even more valuable as your programs grow in complexity.
OOP.fs// Interface definitiontypeICalculator=abstractAdd:x:int->y:int->intabstractMultiply:x:int->y:int->int// Class implementation with interfacetypeCalculator(precision:int)=// Interface implementationinterfaceICalculatorwithmember_.Addxy=x+ymember_.Multiplyxy=x*y// Public methodsmember_.Subtract(x,y)=x-y// Method using propertymember_.RoundToPrecision(value:float)=System.Math.Round(value,precision)// Method with default parametermember_.Power(x:float,?exponent:float)=letexp=defaultArgexponent2.0System.Math.Pow(x,exp)// Object expression (anonymous implementation)letquickCalc={newICalculatorwithmember_.Addxy=x+ymember_.Multiplyxy=x*y}// Type extension - add method to existing typetypeSystem.Int32withmemberx.IsEven=x%2=0Objects Made Simple
F# isfunctional first andimmutable by default, but it also provides pragmatic support for object programming.
Objects Made Simple
F# isfunctional first andimmutable by default, but it also provides pragmatic support for object programming.
- Seamless .NET integration lets you work with existing .NET libraries and frameworks
- Rich interface system allows you to define clear contracts for your components
- Object expressions provide lightweight implementation of interfaces without defining full classes
- Concise member syntax keeps methods and properties clean and readable
- Automatic property generation reduces boilerplate code for data-carrying types
- Type extensions let you add methods to existing types without inheritance
PaymentSystem.fstypeCardInfo={Number:string;Expiry:string;Cvv:string}typeBankInfo={AccountNumber:string;RoutingNumber:string}typePayPalInfo={Email:string;Token:string}typePaymentMethod=|CreditCardofCardInfo|BankTransferofBankInfo|PayPalofPayPalInfotypePayment={Amount:decimalMethod:PaymentMethod}letprocessPaymentpayment=matchpayment.Methodwith|CreditCardcard->printfn"Processing $%.2f via card %s"payment.Amountcard.Number|BankTransferbank->printfn"Processing $%.2f via bank account %s"payment.Amountbank.AccountNumber|PayPalpp->printfn"Processing $%.2f via PayPal account %s"payment.Amountpp.EmailDomain Models made Simple and Safe
F# gives you superb capabilities to create precise domain models that prevent errors at compile time.
Domain Models made Simple and Safe
F# gives you superb capabilities to create precise domain models that prevent errors at compile time.
- Discriminated unions model each payment method with exactly the fields it needs
- No “impossible” states can exist - a credit card payment can’t have a routing number
- Exhaustive pattern matching ensures every payment type is handled properly
- Type safety catches errors at compile time that would be runtime bugs in other languages
By modeling your domain using F#’s algebraic data types, you create self-documenting code where the type system itself enforces business rules. This powerful technique shifts many bugs from runtime to compile time, dramatically improving software reliability.
WebApps.fsopenBrowser.DomopenFeliz// DOM manipulationletbutton=document.createElement("button")button.textContent<-"Click me!"button.addEventListener("click",fun_->window.alert("Hello from F#!"))document.body.appendChild(button)|>ignore// React component (Feliz)letcounter=React.functionComponent(fun()->let(count,setCount)=React.useState(0)Html.div[Html.button[prop.text"-"prop.onClick(fun_->setCount(count-1))]Html.span[prop.textcount]Html.button[prop.text"+"prop.onClick(fun_->setCount(count+1))]])F# for JavaScript and the Full Stack
F# is for both client and server. WithF# web technologies, you can target JavaScript environments directly. This means you can use F# to build web applications, mobile apps, and even serverless functions that run in the cloud.
F# for JavaScript and the Full Stack
F# is for both client and server. WithF# web technologies, you can target JavaScript environments directly. This means you can use F# to build web applications, mobile apps, and even serverless functions that run in the cloud.
- Type-safe DOM manipulation catches errors at compile time, not runtime
- Seamless React integration with hooks and modern patterns
- Full npm ecosystem access with clean TypeScript-like interop
- Simplified async programming with F#’s computation expressions for promises
F# brings its powerful type system and immutability to frontend development, eliminating common JavaScript bugs while maintaining full access to the JavaScript ecosystem.
TypeProviders.fsopenFSharp.DatatypePeopleDB=CsvProvider<"people.csv">letprintPeople()=letpeople=PeopleDB.Load("people.csv")forpersoninpeople.Rowsdo// Access the CSV fields with intellisense and type safety!printfn$"Name: %s{person.Name}, Id: %i{person.Id}"Type-Safe, Integrated Data
F# Type Providers create a seamless bridge between your code and data sources.
Type-Safe, Integrated Data
F# Type Providers create a seamless bridge between your code and data sources.
- Zero-friction data access connects to CSV, JSON, XML, SQL, and more without manual mapping
- Static typing at compile time prevents runtime errors when accessing external data
- Automatic schema discovery creates F# types directly from sample data or schemas
- Full IDE integration provides intellisense for external data sources
- Design-time capabilities validate your code against live data sources before execution
SequenceExpressions.fs// A function generating a sequence of numbersletrecfizzBuzzSeqn=seq{yieldmatchnwith|xwhenx%15=0->"fizzbuzz"|xwhenx%3=0->"fizz"|xwhenx%5=0->"buzz"|_->n.ToString()yield!fizzBuzzSeq(n+1)}// Process the sequence using a pipelinefizzBuzzSeq1|>Seq.take100|>Seq.iter(printfn"%s")Data Pipelines with Sequence Expressions
F# sequence expressions provide compositional, functional stream processing capabilities that integrate seamlessly with every part of the language.
Data Pipelines with Sequence Expressions
F# sequence expressions provide compositional, functional stream processing capabilities that integrate seamlessly with every part of the language.
- Simplified data generation through sequence expressions
- Compositional data processing through library routines
- On-demand evaluation of data streams
- Fluent, maintainable code that is easy to read and understand
AsyncExpressions.fs// An async functionletfetchDataAsyncurl=async{printfn"Fetching data from %s..."urldo!Async.Sleep1000// Simulate network delayreturnsprintf"Data from %s"url}// Using pattern matching in async codeletprocessPersonAsyncperson=async{letresult=validatePersonperson.Ageperson.Namematchresultwith|Okvalidated->return!fetchDataAsync$"profile/{validated.Name}"|Errormsg->return$"Validation error: {msg}"}processPersonAsync{Name="Snowdrop";Age=13}|>Async.RunSynchronouslyAsync Programming made Easy
F# async expressions provide a powerful way to handle asynchronous programming, making it more readable and maintainable. They allow you to write non-blocking code that looks like synchronous code, which is particularly useful for I/O-bound operations.
Async Programming made Easy
F# async expressions provide a powerful way to handle asynchronous programming, making it more readable and maintainable. They allow you to write non-blocking code that looks like synchronous code, which is particularly useful for I/O-bound operations.
- Async expressions provide a clean syntax for defining asynchronous workflows
- Integration with existing libraries makes it easy to use async expressions with other F# features
- Error handling is simplified with the use of discriminated unions and pattern matching
- Seamless integration with F#’s type system ensures type safety and reduces runtime errors
- Support for cancellation and timeouts allows you to manage long-running operations effectively
ComputationExpressions.fs// Define a custom computation expression for validationtypeValidationBuilder()=member_.Bind(x,f)=matchxwith|Okvalue->fvalue|Errore->Erroremember_.Return(x)=Okxmember_.ReturnFrom(x)=xletvalidate=ValidationBuilder()typePerson={Name:string;Age:int}// Use the custom computation expressionletvalidatePersonagename=validate{let!validAge=ifage>=0&&age<150thenOkageelseError"Age must be between 0 and 150"let!validName=ifString.lengthname>0thenOknameelseError"Name cannot be empty"return{Name=validName;Age=validAge}}Clean Code with Computation Expressions
F# computation expressions give you an elegant syntax for compositional control flows with a clean, readable notation that some say is F#’s superpower.
Clean Code with Computation Expressions
F# computation expressions give you an elegant syntax for compositional control flows with a clean, readable notation that some say is F#’s superpower.
- Computation expressions factor out how code is composed together
- Custom control flow abstractions create domain-specific mini-languages
- Seamless error handling withrailway-oriented programming patterns
- Elegant data transformations by hiding boilerplate and focusing on business logic
- Composable workflows that can be combined and nested for complex operations
UnitsOfMeasure.fsopenFSharp.Data.UnitSystems.SI// Acceleration due to gravityletg=9.81<m/s^2>// The return type is inferred as float<m>letdistance(t:float<s>)=0.5*g*t*tletfallDuration=2.0<s>letfallDistance=distancefallDurationprintfn$"Distance fallen in {fallDuration}s is {fallDistance}m"Safe Numbers through Units of Measure
F# offers world-class compile-time unit safety without runtime overhead, giving you the power to express your domain in a type-safe way. This is particularly useful in scientific, engineering and financial applications where unit errors can lead to catastrophic results.
Safe Numbers through Units of Measure
F# offers world-class compile-time unit safety without runtime overhead, giving you the power to express your domain in a type-safe way. This is particularly useful in scientific, engineering and financial applications where unit errors can lead to catastrophic results.
- Compile-time dimensional safety catches errors before running, preventing scientific and engineering mistakes
- Domain-specific units express quantities that directly reflect your problem space
- Automatic unit conversions maintain type safety while handling complex calculations
- Seamless interoperability works with normal numeric types when needed
- Custom unit definitions let you create your own units and conversions with simple syntax
Community
- Join the conversation onBluesky orDiscord
- Participate onReddit
- Contribute to F# projects
We would recommend F# as an additional tool in the kit of any company building software on the .NET stack.
Michael Newton, Senior Developer
F# makes it easy to spend your time answering interesting questions about the domain and less time answering questions about the language.
Jamie Dixon
Around 95% of the code in these projects has been developed in F#
Anton Schwaighofer,Microsoft
Many languages are evolving to be ready for the future ... F# is already there.
Alex Hardwicke
F# will continue to be our language of choice for scientific computing.
Dr. Andrew Phillips
I evaluated F# and found that for certain tasks it was better than C# in terms of performance while maintaining suitable readability
Atalasoft
Large insurance company developed an entire pension quote calculator entirely in F# in under 100 days with no prior F# experience at all...
Large insurance company
The benefits of functional programming in F# have given us a great advantage over our slow moving competitors.
Bayard Rock
Bohdan ... shows F#'s use for performing aggregations over large datasets, taking advantage of CPU and IO parallelism
Bohdan Szymanik
F# encourages Reason Driven Development that leads to virtually bug-free code
Boston-based Financial Services Firm, Fixed Income
F# is the night vision goggles I need when I go into the dark and attempt to solve previously unsolved problems.
Professor Byron Cook
F# allow us to keep the code simple even in complicated business cases.
Urs Enzler
F# is a powerful language and it is great to do cross platform development with it.
Can Erten
At ClearTax, We have built a whole product from the ground-up in F#. It's been running in production for a couple of years — this has been a great experience for us.
Ankit Solanki,ClearTax
The efficient use of functional programming throughout the R&D cycle helped make the cycle faster and more efficient.
Moody Hadi (CME Group)
On a release of a complex rules engine and data transformation system to one of our customers, we were delighted to hear that across 90+ markets, not one of them found any issues with any of the calculations in the datasets. F# just works.
Isaac Abraham, Compositional IT
At Credit Suisse, we've been using F# to develop quantitative models for financial products
Howard Mansell
...your code is less error-prone...
Dario
F# rocks... building out various algorithms for DNA processing here and it's like a drug
Darren Platt
F#...made it trivial...
Prof David Walker
F# brought correct defaults, simplicity and safety back to our coding
Deyan Petrov,5G Pay
There is a noticeable interest in the developer community in Russia towards F#.
Dmitry Soshnikov
I could not recommend F# highly enough – I insist that you try it!
Ben Lynch
F#'s powerful type inference means less typing, more thinking
Don Syme
My team chose F# for its functional paradigm, maturity, and ease of interoperation with the .NET framework
Dylan Hutchison
At a major Investment Bank, we used F# to build an Early Warning Indicator System for Liquidity Risk
Stephen Channell
...we have decided to use F# as our functional language to have automatic integration with rest of the system...
EMEA-based Security Solutions Company
With its new tools, the bank can speed development by 50 percent or more, improve quality, and reduce costs.
Large Financial Services Firm, Europe
I can tell you, F# really saved us a ton of effort.
Giuseppe Maggiore
We see great potential for F# to be used as a scripting language in CAD; it fits very well for computational design challenges in the construction industry.
Goswin Rothenthal
Grange Insurance parallelized its rating engine to take better advantage of multicore server hardware
Grange Insurance
F# terse syntax made the final code look really similar to the algorithm we wrote at first
Green Eagle Solutions
The performance is phenomenal. We can now re-calculate the entire bank portfolio from scratch in less than a second and the response-time for single deal verification calculation is far below 100 milliseconds.
Jan Erik Ekelof, M.Sc.
Solving a number of programming problems using the language convinced me of the supreme qualities of F#
Hans Rischel
When F# is combined with Visual Studio... productivity goes through the roof!
Prof Nigel Horspool
The compiler and the use of exhaustive pattern matching have saved us from what could’ve been many mistakes in production.
Kristian Lundström & Simon Lydell
Using F# for cross-platform mobile development (Android, iOS) saves development time
James Moore
...I have to say I love the language...
Jared Parsons
Type providers made working with external data sources simple and intuitive.
Jon Canning
F# allowed us to mix Domain-Driven Design, Functional Programming and Azure to deliver a high quality web application.
Jorge Fioranelli
F# is more flexible than C#, yet gives stronger type safety. It allows for fearless refactoring, which is also easier because of naturally less coupled code while at the same time codebase being 40%-size of equivalent c# one.
Jozef Rudy, PhD
The F# code is consistently shorter, easier to read, easier to refactor and contains far fewer bugs. As our data analysis tools have developed ... we've become more productive.
Kaggle
The results speak for themselves.
Matt Ball
I keep being surprised by how compact and readable F# is...
London-Based Asset Management Company
The sensible defaults (immutability, non-nullability, algebraic data types, etc.) along with the power of the F# compiler enables our team to quickly and concisely develop systems.
Matt McCarty
Using a full F# stack to provide Server, Browser client and Mobile apps.
Maxime Mangel
Programming in F# feels like writing out ideas rather than code
Maria Gorinova
Everyone gets really amazed when they try F# and experience its immense expressive power
Mário Pereira
With F# I can develop libraries in a fraction of the time.
Mauricio Scheffer
In our engineering group at Microsoft we use F# for several projects
Microsoft Engineering Team
The simple, well-designed and powerful core of the language was perfect for introducing the fundamental concepts of functional programming.
Michael R. Hansen
...We use F# in oceanographic research to connect multiple visualizations together in time and space...
Rob Fatland, Microsoft Research
F# is central to Microsoft’s quantum algorithm research
Dave Wecker
it is fun language to code in
namigop (Erik Araojo)
F# was so easy to pick up we went from complete novices to having our code in production in less than a week.
Jack Mott
...The AI is implemented in F#...
Microsoft,Path of Go
...That's the reason we have chosen F# for our undergraduate functional programming class...
Prof. Peter Sestoft
Anyone who has developed software can appreciate that while a working program is an asset the source code is a liability, especially when working in a regulated industry. F# lets us keep the codebase small and agile while delivering feature-rich and proven to work solutions.
Eugene Tolmachev, Prolucid
The power and flexibility of the language lets us ship features faster, with fewer bugs.
Marty Dill
Many attributes of the F# programming language make it an ideal choice for ...the exponentially growing volumes of molecular analysis data
Dr. Robert Boissy
F# is very popular among my students for the programming projects
Simão Sousa
For a machine learning scientist, speed of experimentation is the critical factor to optimize.
Patrice Simard
The use of F# demonstrates a sweet spot for the language within enterprise software
Simon Cousins
I have now delivered three business critical projects written in F#. I am still waiting for the first bug to come in.
UK-based Power Company
By using F# and its strong type system, we were able to keep the code base consistent and easily adaptable to this ever-evolving and growing project.
Joh Dokler
F#'s language features not only made it a no-brainer for our project, but allowed us to produce composable, deterministic, and concise code.
Stephen Kennedy
F#...levels the playing field between beginners and experienced programmers.
Prof. Susan Eisenbach
"Speed. I am speed." works for F# like a charm.
Sync.Today
...the core logic is written in F# wherever possible...
Andrea D’Intino
We recommend teaching F# because it is an extraordinary and flexible tool for teaching different areas of Computer Science
Antonio Cisternino
I am using F# to develop an API for data encryption using fully homomorphic encryption.
Vitor Pereira
F# proved ideal for the complex data machinations required to build the models from raw Excel input.
A Fortune 100 Manufacturer
The F# solution offers us an order of magnitude increase in productivty...
GameSys
