FP Domain Modeling

Domain modeling with types. Make illegal states unrepresentable, workflows as pipelines, error handling at the type level.

Cross-references: fp-principles | fp-hexagonal-architecture | fp-algebra-driven-design

1. The Two Building Blocks

[STARTER]

All domain types compose from two operations:

• AND (Record Types): Value has ALL of these fields. Order requires CustomerInfo AND ShippingAddress AND OrderLines.
• OR (Choice Types): Value is ONE OF these alternatives. ProductCode is either WidgetCode OR GizmoCode.

Combined recursively, these express virtually any domain structure.