Chapter IV · Lua.ex integration / Lesson 25 of 27 Host integration

Errors across the boundary

You'll learn: Catch Lua.RuntimeException on the Elixir side — line, source, and call stack come along.

Runtime errors in Lua raise Lua.RuntimeException on the Elixir side. The exception carries the offending line, the source snippet, and the call stack. try/rescue catches it; Exception.message/1 formats the pretty version you see in this playground.

Elixir · your app

Reference only

try do
  Lua.eval!(Lua.new(), """
    local function deep(x) return x.missing.field end
    deep(nil)
  """)
rescue
  e in Lua.RuntimeException ->
    IO.puts(Exception.message(e))
    {:error, e.line, e.source}
end

Output idle

Hit Run to execute.

Try it: Change nil to { missing = { field = 42 } } and the error disappears — you get 42 back. Now toggle Bytecode and find the get_table op that the runtime stack points at.