#!/usr/bin/lua
-- List the dependencies of a function, i.e. the values it uses from
-- outside its own scope. Not sure if this works for upvalues.
-- by Kragen Javier Sitaker, written 2009, dedicated to the public domain
-- (i.e. I abandon all copyright in the work 
-- so that anyone may use it for any purpose)

function dependency_grabbing_metatable(target)
   local metatable = {}
   local dependencies = {}

   function metatable.__index(_, key) 
      dependencies[key] = true
      return target[key] 
   end

   function metatable.__newindex(_, key, value)
      dependencies[key] = true
      target[key] = value 
   end

   return metatable, dependencies
end

function read_logging_proxy(target)
   local proxy = {}
   local metatable, dependencies = dependency_grabbing_metatable(target)
   setmetatable(proxy, metatable)
   return proxy, dependencies
end

-- Return a table of the global variables accessed by calling a function.
function get_dependencies(func, ...)
   local orig_env = getfenv(func)
   new_env, dependencies = read_logging_proxy(orig_env)
   setfenv(func, new_env)
   func(...)
   setfenv(func, orig_env)
   return dependencies
end

-- for demo:
vowels = { a=true, e=true, i=true, o=true, u=true }
function is_consonant(char)
   char = string.lower(char)
   if char < 'a' or char > 'z' then return false end
   return not vowels[char]
end      

function demo()
   for _, char in ipairs {'@', 'x', 'a'} do
      print('calling is_consonant with '..char..'; dependencies: ')
      for var in pairs(get_dependencies(is_consonant, char)) do
         print('', var)
      end
   end
end