Re: Coroutines & Iterators

[RLake@...]

> The Lua5 manual begins its definition of coroutines this way:

>      Lua supports coroutines, also called semi-coroutines, generators, or
>      colaborative multithreading.

> And describes the new "for" syntax this way:

>      The generic for statement works over functions, called generators.
It
>      calls its generator to produce a new value for each iteration,
>     stopping when the new value is nil.

<<SNIP>>

Lua does not call coroutines "generators" but in the world at large
coroutines
are also called "generators".

Lua calls functinos used in the generic for statement "generators"

I admit that the documentation could be improved, but I think it is
technically accurate.

> And how do iterators control their state if they don't control when they
> yield...?

They stash it somewhere, quite possibly in a closure.

> > I am passing this one as I don't know what this "wrap" is about.

> I gave examples like:

>      withOutputToFile() do
>            -- write stuff
>      end

> with the implementation:

>      function withOutputToFile( file )
>            writeto( file )
>            yield()
>            writeto()
>      end

> This doesn't yield any value, it just "wraps" the call to the
block--which
> is really just an anonymous function.

> This idiom is useful anytime resources must be protected.

You could do this with a carefully crafted for-generator. The
implementation is left as an exercise to the reader.

R.