eskil / luerl_map_to_function

Example of an issue with doing function table maps in luerl

LuerlMapToFunction

This example demonstrates an issue with calling functions returned in a table.

For instance, if you want to get a function table;

function get_function_table()
  table = {}
  table["increment"] = do_increment
end

state = 0
function do_increment()
  state = state + 1
  return state
end

Obtaining the map and calling increment (aka do_increment) from luerl does not provide an obvious way to pass in & update lua_state.

To get the table;

{[lua_map], _lua_state} = :luerl.call_function([:get_function_table], [], lua_state)
ex_map = Map.new(lua_map)
function = ex_map["increment"]
[number] = function.([]) # How can the state be threaded through?

Build and run

mix deps.get
mix deps.compile
mix escript.build
./luerl_map_to_function

The output (ignoring the Function.info output) is;

./luerl_map_to_function
lua: number is 2 (should be 2)
elixir number = 3 (should be 3)
function #Function<6.93491019/1 in :luerl.decode/3>
function info [
    pid: #PID<0.99.0>,
  module: :luerl,
  new_index: 6,
  new_uniq: <<51, 204, 154, 21, 95, 68, 126, 176, 146, 163, 10, 159, 121, 165,
    177, 253>>,
  index: 6,
  uniq: 93491019,
  name: :"-decode/3-fun-0-",
  arity: 1,
  env: [... lua state at capture time it seems..]
  type: :local
]
elixir number = 4 (should be 4)
elixir number = 4 (should be 5)

The two last calls are from elixir to lua via the bound function. It does use the right initial state (3) in the first call, but since the lua state isn't passed in, it's not updated and the next call still sees the first state.