Compiling chunks

Mix.install([
  {:lua, "~> 1.0.0-rc.0"}
])

Compile once, run many times

Lua.load_chunk!/2 parses and compiles a string into a reusable %Lua.Chunk{}. Compilation happens once; passing the chunk to Lua.eval!/2 skips parsing and compilation on every run — useful for a template or rule evaluated per request.

The VM we compile against doesn’t have to be the one we run against later.

{chunk, _lua} = Lua.load_chunk!(Lua.new(), "return greeting .. name .. '!'")
chunk.__struct__

Lua.Chunk

Each run uses a fresh state with different globals, so the same compiled chunk produces different results.

for name <- ["Ada", "Grace", "Edsger"] do
  state =
    Lua.new()
    |> Lua.set!([:greeting], "Hello, ")
    |> Lua.set!([:name], name)

  {[message], _lua} = Lua.eval!(state, chunk)
  message
end

["Hello, Ada!", "Hello, Grace!", "Hello, Edsger!"]

Surfacing syntax errors early

Lua.parse_chunk/1 pre-parses a script so you can surface syntax errors before ever running anything. It returns {:ok, chunk} on success and {:error, messages} with human-readable diagnostics on failure.

{:error, [message]} = Lua.parse_chunk("return 1 +")
IO.puts(message)

Parse Error

  at line 1, column 11:

  Expected expression


   1 │ return 1 +
                 ^

Suggestion:
  Reached end of file unexpectedly. Check for missing 'end' keywords or closing delimiters.