Quick Lua Promises (v0.1)

promise.lua

Promise = (function(asyncFunction)

  local state = 'pending';
  local result;
  local rListen, eListen = {}, {};

  asyncFunction(function(...)
    for _,f in pairs(rListen) do
      f(...);
    end;
  end, function(err)
    for _,f in pairs(eListen) do
      f(err)
    end
  end);

  return setmetatable({
    next = function(promise, nextFunction, errorFunction)
      return Promise(function(resolve, reject)
        local function nf(r) resolve(nextFunction(r)); end;
        if(state == 'resolved' and type(nextFunction) == 'function') then nf(table.unpack(result)); end;
        if(state == 'error' and type(errorFunction) == 'function') then errorFunction(table.unpack(result)); end;
        if(state == 'pending') then
          table.insert(rListen, nf);
          table.insert(eListen, errorFunction);
        end;
      end);
    end
  }, {
    __tostring = function(t)
      return('promise: ' .. tostring(asyncFunction):match(': (.*)'));
    end
  });

end);