Re: Hi, I am a little confused about stateless iterator.

> Message: 7
> Date: Mon, 16 Dec 2013 14:46:10 -0500
> From: Tom N Harris <telliamed@whoopdedo.org>
> Subject: Re: Hi, I am a little confused about stateless iterator.
> To: lua-l@lists.lua.org
> Message-ID: <1431849.AMzBL4T3Ev@green>
> Content-Type: text/plain; charset="us-ascii"
>
> Your stateful function is wrong. It's stateful because the iterator keeps a
> private state. This means the third value, the initial state, is not used. The
> version you wrote will be invoked with i=0 the first time, then i=min, then
> i=min+min, etc.
>
> Fixed version is:
>
> > --stateful
> > --[[
> > function fromto(n,m)
> > local r = m - n
> > local i = -1
> > return function()
> > i = i + 1
> > if i < r then
> > return n + i
> > else
> > return nil
> > end
> > end
> > end
> > --]]
>
> Your stateless iterator is correct. The function receives the state variable
> from the invoker which it mutates then passes back. Each time the iterator
> receives the result of the previous iteration, which is suitable when each
> element in the sequence is derived from the previous element. If you need more
> state than what the iterator returns, you need to be stateful. For instance,
> you couldn't generate a Fibonacci sequence with a stateless iterator. No,
> that's not true. But it would look like:
>
> for _,n in fibonacci() do print(n) end
>
> Where _ is a table or closure. But if you're going to create the garbage
> anyway, you may as well make the iterator a closure.

Thanks for your explanation.