Undefined Functions

I want to write a program that can run with or without an api.

Whenever i run it without the api loaded, i get an error at the first function call.

If i wanted to do this with some variable, i would do something like this:

function do_something(var)
	if not var then
		--do it without var
	else
		--use var
	end
end

Is there a way for me to do this with an API function that may or may not be loaded?

i was thinking maybe a second API that gives function pointers, but then that would have the same problem.

APIs are tables and functions are variables.

if API and API.somefunction then
  --# do one thing
else
  --# do another
end

Thanks!