From: Jim Weirich <jweirich@...>
Date: 2003-03-25T20:42:50+09:00
Subject: Re: Iterate over two lists in parallel

On Tue, 2003-03-25 at 02:26, Hal E. Fulton wrote:

> Sprry to reply to my own post, but another
> small issue is that the generator always
> returns nil after it exhausts the collection.
> 
> But what if a collection contains nil values?
> 
> I think I'd like an 'end?' method or something.
> At worst, we could define a meta-nil value, but
> I'm betting that's not necessary.

Yeah, my tutorial glossed over that part.  Having a standard for
external iterators will really help them be more useful.  I would
suggest more? instead of end?.  This allows you to write loops in terms
of the positive rather than a negative test.  I.e.

   while it.more?

Python iterators throw an exception when they are done.  This means you
have one less method call to make in a loop.  I'm uncomfortable with the
exception, it seems to be premature optimization.  However, if you do go
that route, then I like Julian's use of catch/throw over an exception
(exceptions in my mind indicate a failure).

-- 
-- Jim Weirich     jweirich@one.net    http://w3.one.net/~jweirich
---------------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct, 
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)