Re: (not) handling new programming idioms with grace

[Dirk Laurie <dirk.laurie@...>]

2018-07-15 16:22 GMT+02:00 John Belmonte <john@neggie.net>:
> It's been about 10 years since my post "state of the Lua nation on resource
> cleanup" [1].  The only relevant thing that's happened in this area since
> then was Lua getting pcall + coroutine love in 5.2.
>
> My position on Lua's need for some type of scope exit hook is only stronger
> these days.  It's not just about resource cleanup.  For example, there are
> some very interesting concurrency and cancellation control structures being
> developed as Python libraries [2] [3] which would be cumbersome and much
> less effective in a language lacking the equivalent of Python's "with"
> statement.
>
> To summarize the concurrency control structure, called a "nursery": all
> spawned tasks within the scope block are owned by that scope's context
> manager, and the scope will not end until all child tasks are completed.  If
> a child has an exception, all other child tasks will be cancelled and the
> error will be propagated.  I'm well versed in trying to use Lua function
> lambdas for this kind of problem.  The result is not satisfying.

I don't quite understand the problem, and maybe my ignorance shows,
but ...

What does a 'with' structure achieve that

repeat
  local whatever
...
  if exception then break end
...
until false

does not?