From: Nat Pryce <nat.pryce@...13media.com>
Date: 2002-11-19T23:44:32+09:00
Subject: Re: Thoughts on generators

On Tue, 2002-11-19 at 12:49, Martin DeMello wrote:
> ....it might be useful to see where we *can* efficiently write
> 
>   g = SimpleGenerator.new(a) # should be space-efficient
>   i = g.next # should be O(1) and cheap
>   
> and where the generator iterates over the sequence nondestructively,
> so that it is threadsafe. One could use g.val rather than g.next,
> depending on how you think of it.
> 
> SimpleGenerator.new would most likely need to be a factory that
> instantiated more specific per-type generators. Some easy examples for
> generator-generating objects:
> - arrays and other structures that support a[i] where i is an integer
> (initialize sets @i = -1, and .next does an @i+=1, @array[@i].dup)
> - functions on integers (.next returns f(@i))
> - sequences where f[i+1] = g(f[i], f[i-1], ..) and which don't depend
> on too large a history (the Fibonacci sequence, e.g., or a random
> number generator)
> - generator-only structures like unbounded lists and circular arrays

If the behaviour of SimpleGenerator.new(a) depends on the type of a --
e.g. is polymorphic with respect to a -- then it should really be a
method defined by a.

E.g. your example would be reformulated as:

    g = a.generator
    i = g.next

Cheers,
	Nat.

-- 
Nat Pryce <nat.pryce@b13media.com>
B13media