Errors, Pcall, and Effects

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 local values and calls example make visible?

local function stamp()
  return runtime.time_now_unix_ms()
end

let runtime := import "@std/runtime";

export let stamp () : Int := request runtime.timeNowUnixMs();

Reading Errors, Pcall, and Effects from Lua

On the Musi side, Musi lets a calculation be a let, a function, or a final expression without wrapping it in an object or framework first. 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 preserve call ceremony just because the source language needs it for methods, receivers, overloads, or closures. 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 receipt total, label, distance, or score is pure data moving through named calls. The Lua instinct still helps here: Keep the Lua habit of using small names and simple values.

Keep close

• Effects
• Using
• Handlers