F#

F# is the functional sibling of C# on .NET. v9.0 (2025) brings Nullable Reference Types integration and better performance for list comprehensions.

When to Use

• Financial Tech: Correctness and domain modeling.
• Data Processing: Pipeline operator |> and immutability by default.
• Interpro: Seamlessly use any NuGet package.

Core Concepts

Discriminated Unions

type Shape = Circle of float | Rect of float * float.

Pipe Operator

data |> filter |> map.

Computation Expressions

async { ... }, task { ... }.

Best Practices (2025)

Do:

• Use Records: Immutable data containers.
• Use Pattern Matching: match x with ....
• Use SAFE Stack: For full-stack F# web apps (Saturn, Azure, Fable, Elmish).

Don't:

• Don't mimic C#: Avoid classes/inheritance unless interoperating.

References

• F# Guide