Learn Fsharp - 10 Code Examples & CST Typing Practice Test

F# is a functional-first, strongly typed language on the .NET platform. It blends functional, object-oriented, and imperative styles, offering concise syntax, powerful type inference, and high reliability. Ideal for data science, finance, domain modeling, and backend services.

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F# Counter and Theme Toggle F# Simple Calculator F# Factorial F# Fibonacci Sequence F# List Comprehension F# Map Filtering F# Anonymous Functions F# Reduce Example F# Zip and Map F# Pattern Matching on Tuples

Learn FSHARP with Real Code Examples

Updated Nov 18, 2025

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Code Sample Descriptions

F# Counter and Theme Toggle

let mutable count = 0
let mutable isDark = false

let updateUI() =
    printfn "Counter: %d" count
    printfn "Theme: %s" (if isDark then "Dark" else "Light")

let increment() = count <- count + 1; updateUI()
let decrement() = count <- count - 1; updateUI()
let reset() = count <- 0; updateUI()
let toggleTheme() = isDark <- not isDark; updateUI()

// Simulate actions
updateUI()
increment()
increment()
toggleTheme()
decrement()
reset()

Demonstrates a simple counter with theme toggling using F# variables and console output.

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F# Simple Calculator

let add a b = a + b
let subtract a b = a - b
let multiply a b = a * b
let divide a b = a / b

printfn "Add 5 + 3: %d" (add 5 3)
printfn "Subtract 5 - 3: %d" (subtract 5 3)
printfn "Multiply 5 * 3: %d" (multiply 5 3)
printfn "Divide 6 / 2: %d" (divide 6 2)

Demonstrates basic arithmetic operations using functions.

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F# Factorial

let rec factorial n =
    if n <= 1 then 1
    else n * factorial (n - 1)

printfn "Factorial of 5: %d" (factorial 5)

Recursive factorial function in F#.

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F# Fibonacci Sequence

let rec fibonacci n =
    if n = 0 then 0
    elif n = 1 then 1
    else fibonacci(n-1) + fibonacci(n-2)

[0..9] |> List.iter (fun n -> printfn "%d" (fibonacci n))

Recursive Fibonacci sequence generator.

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F# List Comprehension

let numbers = [1..10]
let squares = [for n in numbers do if n % 2 = 0 then yield n * n]
printfn "%A" squares

Using list comprehension to square even numbers.

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F# Map Filtering

let scores = dict ["Alice",10; "Bob",5; "Charlie",12]
let highScores = scores |> Seq.filter (fun kv -> kv.Value >= 10) |> dict
printfn "%A" highScores

Filtering a map based on values.

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F# Anonymous Functions

let add = fun x y -> x + y
printfn "%d" (add 3 7)

Using anonymous functions and piping.

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F# Reduce Example

let numbers = [1;2;3;4;5]
let sum = List.fold (fun acc x -> acc + x) 0 numbers
printfn "%d" sum

Summing a list of numbers using List.fold.

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F# Zip and Map

let xs = [1;2;3]
let ys = [4;5;6]
let sums = List.map2 (+) xs ys
printfn "%A" sums

Combining two lists using zip and map.

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F# Pattern Matching on Tuples

let addPair (x,y) = x + y
printfn "%d" (addPair (3,7))

Using pattern matching to destructure tuples.

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Frequently Asked Questions about Fsharp

What is Fsharp?

What are the primary use cases for Fsharp?

Financial modeling and trading systems. Data science and ML workflows. Backend microservices on .NET. Domain-driven design (DDD). Scientific computation. Scripting & automation. High-reliability enterprise applications

What are the strengths of Fsharp?

Concise & expressive code. Enterprise-grade reliability on .NET. Strong static typing with inference. Excellent for domain modeling. Great for data processing & analysis

What are the limitations of Fsharp?

Smaller community than C#/Python. Not ideal for UI-heavy applications. Learning curve for functional thinking. Corporate teams often prefer C#. Tooling is improving but not perfect

How can I practice Fsharp typing speed?

CodeSpeedTest offers 10+ real Fsharp code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.

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Learn Fsharp - 10 Code Examples & CST Typing Practice Test

Code Sample Descriptions

F# Counter and Theme Toggle

let mutable count = 0
let mutable isDark = false

let updateUI() =
    printfn "Counter: %d" count
    printfn "Theme: %s" (if isDark then "Dark" else "Light")

let increment() = count <- count + 1; updateUI()
let decrement() = count <- count - 1; updateUI()
let reset() = count <- 0; updateUI()
let toggleTheme() = isDark <- not isDark; updateUI()

// Simulate actions
updateUI()
increment()
increment()
toggleTheme()
decrement()
reset()

Demonstrates a simple counter with theme toggling using F# variables and console output.

Let’s Try →

F# Simple Calculator

let add a b = a + b
let subtract a b = a - b
let multiply a b = a * b
let divide a b = a / b

printfn "Add 5 + 3: %d" (add 5 3)
printfn "Subtract 5 - 3: %d" (subtract 5 3)
printfn "Multiply 5 * 3: %d" (multiply 5 3)
printfn "Divide 6 / 2: %d" (divide 6 2)

Demonstrates basic arithmetic operations using functions.

Let’s Try →

F# Factorial

let rec factorial n =
    if n <= 1 then 1
    else n * factorial (n - 1)

printfn "Factorial of 5: %d" (factorial 5)

Recursive factorial function in F#.

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F# Fibonacci Sequence

let rec fibonacci n =
    if n = 0 then 0
    elif n = 1 then 1
    else fibonacci(n-1) + fibonacci(n-2)

[0..9] |> List.iter (fun n -> printfn "%d" (fibonacci n))

Recursive Fibonacci sequence generator.

Let’s Try →

F# List Comprehension

let numbers = [1..10]
let squares = [for n in numbers do if n % 2 = 0 then yield n * n]
printfn "%A" squares

Using list comprehension to square even numbers.

Let’s Try →

F# Map Filtering

let scores = dict ["Alice",10; "Bob",5; "Charlie",12]
let highScores = scores |> Seq.filter (fun kv -> kv.Value >= 10) |> dict
printfn "%A" highScores

Filtering a map based on values.

Let’s Try →

F# Anonymous Functions

let add = fun x y -> x + y
printfn "%d" (add 3 7)

Using anonymous functions and piping.

Let’s Try →

F# Reduce Example

let numbers = [1;2;3;4;5]
let sum = List.fold (fun acc x -> acc + x) 0 numbers
printfn "%d" sum

Summing a list of numbers using List.fold.

Let’s Try →

F# Zip and Map

let xs = [1;2;3]
let ys = [4;5;6]
let sums = List.map2 (+) xs ys
printfn "%A" sums

Combining two lists using zip and map.

Let’s Try →

F# Pattern Matching on Tuples

let addPair (x,y) = x + y
printfn "%d" (addPair (3,7))

Using pattern matching to destructure tuples.

Let’s Try →

Frequently Asked Questions about Fsharp

What is Fsharp?

What are the primary use cases for Fsharp?

What are the strengths of Fsharp?

Concise & expressive code. Enterprise-grade reliability on .NET. Strong static typing with inference. Excellent for domain modeling. Great for data processing & analysis

What are the limitations of Fsharp?

Smaller community than C#/Python. Not ideal for UI-heavy applications. Learning curve for functional thinking. Corporate teams often prefer C#. Tooling is improving but not perfect

How can I practice Fsharp typing speed?

CodeSpeedTest offers 10+ real Fsharp code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.