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- Subject: Re: Nested iterators, how to best implement?
- From: Jerome Vuarand <jerome.vuarand@...>
- Date: Thu, 29 Jan 2015 15:03:51 +0000
2015-01-29 14:13 GMT+00:00 Tony Papadimitriou <firstname.lastname@example.org>:
> I’m looking for the best (?) general way to implement *nested* iterators in
> Lua (5.3, of course).
> For example: I have an iterator that returns single items when used in a
> FOR .. IN loop. Each item is treated somehow but that loop, and the result
> I want it to become available in another iterator.
> Easy, but I do NOT want to store all intermediate results in a table, and
> then traverse the table again, as the size of the table could be too large
> or even unknown while the iterator is running (until some condition happens
> that terminates it).
> In Python 3, for example, this would be very simple with each routine using
> YIELD instead of RETURN, and iterators can be nested to an arbitrary level.
> But, in Lua, I can’t seem to find an obvious (memory efficient) solution.
> (I would love for Lua to have the same simplicity in this regard.)
> Perhaps explicit use of co-routines is one solution, but maybe there is a
> more immediate way I missed.
> Maybe someone can point me to some example.
You can use coroutine.yield like in Python, and use coroutine.wrap to
create coroutines easily. For example:
local yield,wrap = coroutine.yield,coroutine.wrap
local function integers(count)
for i=1,count do
local function evens(count)
for i in wrap(integers), count do
yield(i * 2)
local function odds(count)
for i in wrap(evens), count do
yield(i + 1)
for i in wrap(odds), 12 do
Short of custom language modification I can't imagine any simpler syntax.