Re: Try-catch and try-finally

[Peter Melnichenko <mpeterval@...>]

My somewhat unfinished version: https://github.com/mpeterv/goodcall

Pros:
* Supports Python's `else` block, which is executed only if `try` block
  didn't throw.
* Allows rethrowing without losing original traceback.
* Supports yielding from protected blocks a-la coxpcall, but unlike it
  doesn't lose tracebacks in any case.

Cons:
* Rethrown errors are tables {err, traceback}.
  If some errors are part of an API, users have to know how to check
  if an error is wrapped and how to unwrap it. Or they have to use my
module, too.
* Rethrown errors have __tostring metamethod to make them look nice
  when caught by something that just prints errors. Unfortunately, Lua
interpreters
  for different versions handle such table errors differently, with
Lua 5.1 replacing
  it with `(error object is not a string)`.

-- Peter