Using part of a Lua script from C

[Evan Burkitt <evanb@...>]

I have an application that calls functions in Lua scripts from C (C++, 
actually). My design expects a certain function, "filter()", to exist in 
the scripts it uses. filter() typically calls other functions in the 
script as part of its behavior, but the C/C++ code doesn't know of or 
use these other functions.

The scripts also contain a section of code that calls filter(). This 
exists so the script as a whole can be run stand-alone via the lua 
command line.

Here's a minimal illustration of what my lua script looks like:
--internal functions:
function internal1() end
function internal2() end

--function called by C/C++:
function filter(a,b)
  internal1()
  internal2()
end

--code to allow the script to run stand-alone:
a = 1
b = 2
filter(a,b)

When I load and compile the script via luaL_loadfile() and lua_pcall(), 
the code at the end begins to execute when I call lua_pcall().

My question is, what is the best way to process the script file so that 
my C/C++ code can call filter() yet the entire script does get executed 
in the process?

-evan