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On 25-Aug-05, at 3:33 PM, William Trenker wrote:

I've been experimenting with introspection in Lua (5.0.2).  If I
understand correctly, a function's parameters are not included in that
function's environment table.  For example:

That's correct. They are local variables.

What I find curious is what happens when I redfine the function in the
same chunk:

You've set p in the global environment.

The environment table is just a table; when a function closure is created, it is created with the same environment table as its creator (*not* a copy of the table):

------------------------ chunk -----------------------
function f(p)  -- same as previous chunk
    local env = getfenv(1)
-- env is now the global environment
    setmetatable(env, {__index=_G})
    env.p = p
-- so this sets p in the global environment
    setfenv(1, env)
    print(string.format("<%s>: p = %s", tostring(f),p))
    print(string.format("<%s>: getfenv(1).p = %s",tostring(f),

What you probably wanted to do was:

function f(p)
  local env = {}  -- a new table
  setmetatable(env, {__index = _G})
    -- now the global environment is the "backup" for the new table
  env.p = p
  setfenv(1, env)
  -- now the function has a different environment table
  -- ...

The following is identical but maybe not so easy to read:

function f(p)
  setfenv(1, setmetatable({p = p}, {__index = _G}))
  -- ...