Blocks, Branching, and Repetition

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 branching and block results example make visible?

local function delivery_fee(distance_km)
  if distance_km == 0 then
    return 0
  end
  return 45
end

let deliveryFee (distanceKm : Int) : Int := match distanceKm (
| 0 => 0
| _ => 45
);

deliveryFee(3);

Reading Blocks, Branching, and Repetition from Lua

On the Musi side, Musi blocks and matches are expressions when they produce a value; the branch answer matters more than the statement container. 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 carry over temporary variables whose only job was to smuggle a branch result out of a statement block. 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 this shape when a route fee, access decision, or small rule table chooses one value from several cases. The Lua instinct still helps here: Keep the Lua habit of using small names and simple values.

Keep close

• Blocks and expressions
• Patterns
• Operators