fsharp-shared

Define shared domain types using F# records and discriminated unions in src/Shared/Domain.fs, then specify API contracts and DTOs in src/Shared/Api.fs. This creates a single source of truth for data models across client and server boundaries, ensuring type safety and consistency.

Use F# records for DTOs and the ITodoApi interface pattern to define CRUD contracts. Records provide immutability and pattern matching support, while interfaces establish clear client-server boundaries with strongly-typed request and response shapes.

Discriminated unions model domain variants exhaustively, eliminating invalid states; option types encode nullability explicitly. Together they enforce type safety at compile time, reducing runtime errors and making domain logic self-documenting through F#'s type system.

Centralize domain types when starting new features or modifying entities to prevent client-server desynchronization. A shared Domain.fs eliminates manual synchronization, reduces bugs from schema drift, and makes type contracts enforceable across boundaries.

Yes. This approach integrates with F# functional patterns—records are immutable by default, option and result types encode effects explicitly, and discriminated unions enable exhaustive pattern matching for domain logic, aligning with functional design principles.

Shared contracts create a single authoritative type definition reducing duplication and drift; separate modules risk inconsistency and require manual synchronization. Shared types enforce compile-time correctness across boundaries and simplify maintenance for full-stack applications.