A C# reader brings habits from nullable flow analysis, records, LINQ, async tasks, extension methods, interfaces, namespaces, and attributes. That helps with domain code through named APIs and tooling feedback, but the Musi page asks a narrower question: what contract should this named cases and pattern matching example make visible?
enum TrafficLight { Red, Yellow, Green }
static bool CanWalk(TrafficLight light) =>
light is TrafficLight.Green;let TrafficLight := data {
| Red
| Yellow
| Green
};
let canWalk (light : TrafficLight) : Bool :=
match light (
| .Green => 0 = 0
| _ => 0 = 1
);Reading Unions and Pattern Matching from C#
On the Musi side, Musi data variants name the cases directly, and match reads the case split at the point where the answer is chosen. Read the shared example through C# eyes: keep the useful instinct, then let Musi name shape, behavior, absence, and outside work in separate places.
False friend
Do not keep integer tags, string unions, subclass checks, or table marker fields when a data variant is the real shape. For a C# reader, the trap is mapping Musi classes to object classes or service containers; Musi class is a typeclass-style behavior contract, not a CLR class with fields, constructors, and inheritance.
When this pays off
Use data variants when an order, animal, traffic light, payment state, or parser result has a closed set of cases. The C# instinct still helps here: Keep the C# habit of making api shape readable at the call site.