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I another post Mike Pall profiled coroutine code and found that it uses more time then he'd like:

> Especially because the latter needs an additional call
> frame (which could be improved by making yield a keyword/VM op).

On a related note, I wonder if it would be at all possible to optimise tailcalls any further? Consider the following functions to sum an arithmetic sequence:

local function sumi(n, r)
  while r > 0 do
    n = n + r
    r = r - 1
  return n

local function sumr(n, r)
  if r > 0 then
    return sumr(n + r, r - 1)
  return n

The recursive sumr takes about 2.5 times more time than the iterative sumi in 5.0.2. (In 5.1-w5 both are quicker, but the iterative version more so than the recursive one...) If tailcalls get cheaper, they would gain in strength as "structured goto's".

Just wishful thinking probably...  ;-)