A Lua reader brings habits from tables, metatables, nil, coroutines, embedding, modules, and small runtime boundaries. That helps with simple data and host/runtime edges without much ceremony, but the Musi page asks a narrower question: what contract should this named cases and pattern matching example make visible?
local TrafficLight = { red = "red", yellow = "yellow", green = "green" }
local function can_walk(light)
return light == TrafficLight.green
endlet TrafficLight := data {
| Red
| Yellow
| Green
};
let canWalk (light : TrafficLight) : Bool :=
match light (
| .Green => 0 = 0
| _ => 0 = 1
);Reading Pattern Matching and Data Variants from Lua
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 Lua 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 Lua reader, the trap is letting table shape, missing fields, and behavior conventions blur together; Musi class is not a metatable pattern; records/data hold table-like shape, classes/instances name promised behavior.
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 Lua instinct still helps here: Keep the Lua habit of using small names and simple values.