Comments and Style

Comments

// A single-line comment
let taxRate = 0.2 // after code

(*
   A block comment
   spanning several lines
*)

/// Returns the price including tax.
/// <param name="price">The net price.</param>
let withTax price = price * (1.0 + taxRate)

printfn "%.2f" (withTax 100.0)

120.00

Comments starting with /// are XML documentation comments: editors show them when you hover over the function, and they're included in generated library documentation. A plain /// line with no tags works too.

Style guidelines

The official F# style guide (on learn.microsoft.com) and the formatter Fantomas agree on these conventions:

• Four-space indentation, spaces only.
• camelCase for values, functions, and parameters; PascalCase for types, modules, union cases, record fields, and namespaces.
• Put each pipeline step on its own line, starting with |>.
• Prefer immutable values and pure functions; keep mutable local.
• Keep functions small and name them after what they return (totalPrice), or what they do if they have side effects (saveOrder).
• Handle every case in a match — never ignore the incomplete-match warning.
• Use option instead of null, and decimal for money.
• Put the "data" parameter last so functions work with |>.

Tools

• Fantomas — formats code automatically (dotnet tool install fantomas, then dotnet fantomas .).
• Ionide / Rider — inline type hints, errors, and refactorings.
• FSharpLint and F# analyzers — catch style issues and common mistakes.

What's next

You now know the core of F#. Try the Beginner Projects, then continue to Level 2 — Intermediate, which starts with records.