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- Subject: Re: Coroutines & Iterators
- From: MichaelL@...
- Date: Wed, 8 Jan 2003 12:55:33 -0500
> The only way to yield values is through coroutine.yield,
> etc. And how do iterators control their state if they
> don't control when they yield...?
Hang on--I think I see what they're doing:
A for statement like
for var_1, ..., var_n in explist do block end
is equivalent to the code:
local _f, _s, var_1, ..., var_n = explist
while 1 do
var_1, ..., var_n = _f(_s, var_1)
if var_1 == nil then break end
In effect, it looks like vars are popped onto the stack and passed *back
into* the "generator." That's how the generator maintains state. So I think
I was confused because the documentation uses "generator" to describe two
Ok, I'll have to think about this a bit more. I think my suggestion still
stands, though, as a way to make the use of anonymous functions "more
natural"--and that in turn leads to what I think is a more natural
implementation of iterators. (Indeed, you no longer need this special "for"
syntax--and it becomes easy to implement a "withOutputToFile" that *feels*