Re: Lua 5 getglobals

[Roberto Ierusalimschy <roberto@...>]

> In a particular function I want to retrieve the globals table of the
> _calling_ function, so I do a getglobals(2).  (I want to "switch" to the
> caller's context.)  However, sometimes this does _not_ return the callers
> globals!  After some fiddling I tracked  the problem down to Lua's use of
> optimized tail calls.  Because tail calls reuse a stackframe instead of
> creating a new one, a getglobals(n) will effectively skip all tail calls and
> end up at a higher level than expected.
> 
> Is there a way around this, or is there another (better) way to get the
> callers globals table?

There is no way around this. The essence of proper tail call is to keep
no information about a function that does a tail call. However, we can
keep a counter, so that Lua will know about the tail calls, and will
keep stack levels correct. Then, a call to "getglobals(n)" where "n" did
a tail call may at least raise an error (avoiding the "fiddling").

-- Roberto