Fsharp Coding Practices

F# Coding Practices

Application skill for F# component design learning (from the archived awesome-guidelines style capsules). When targeting C# consumers, prioritize vanilla.NET API rules over F#-only idioms on the public surface.

Core Principle

F# library quality is audience-shaped APIs, F#-facing modules and unions internally, BCL-friendly types and delegates on cross-language boundaries.

When to Use / NOT

• F# libraries, SDKs, and shared .fs components consumed by F# or other.NET languages.
• Setting up Fantomas, XML doc warnings, .fsi for stable APIs, dotnet build/test in CI.

NOT when:

• Pure C# projects, use csharp-coding-practices.
• Generated FSharp.Core dependents only, validate hand-written public API.

Workflow

1. Names & docs,.NET casing, /// XML, .fsi if stable (fsharp-style-naming-documentation.md).
2. Modules & types, encapsulation, DUs, interfaces (fsharp-style-modules-types.md).
3. Functions & async, Async naming, extensions, constraints (fsharp-style-functions-async.md).
4. Interop, Func, IEnumerable, Task, null guards (fsharp-style-dotnet-interop.md).
5. Verify, Fantomas, dotnet build, optional C# consumer compile check on public API.

Red Flags

• Public modules in cross-language NuGet libraries
• Exposed record/union cases on evolvable types
• Implementation inheritance for extension
• Custom symbolic operators without named API
• Public type abbreviations with wrong semantics
• SRTP/duck constraints on general consumer APIs
• list/Map/option in vanilla.NET public signatures
• Curried or tuple-returning public methods for C# consumers
• int -> int instead of Func<int,int> on public API
• Missing XML docs on exported members
• Overuse [<AutoOpen>]
• No null checks at vanilla.NET boundaries
• [<CLIEvent>] missing on public events

Verification

• dotnet format / Fantomas check (project config)
• dotnet build with XML documentation warnings as errors (if enabled)
• Reflect or C# snippet compile against public API
• Capsule checklist on F#-facing vs vanilla.NET audience

References

• awesome-guidelines/references/fsharp-style-learning-note.md
• awesome-guidelines/references/fsharp-style-naming-documentation.md
• awesome-guidelines/references/fsharp-style-modules-types.md
• awesome-guidelines/references/fsharp-style-functions-async.md
• awesome-guidelines/references/fsharp-style-dotnet-interop.md