From: Robert Dober <robert.dober@...>
Date: 2009-06-23T17:45:06+09:00
Subject: Re: map shall not return an Enumerator ( was re guru help )

On Tue, Jun 23, 2009 at 3:32 AM, David A. Black<dblack@rubypal.com> wrote:
<snip>>
It would buy me
coll.send_to_elements( :+ , 42 )
coll.send_to_elements.join( ", ")
versus
coll.map{ |x| x + 42 }
coll.map{ |x| x.join( ", ") }
it is not so much about typing (although nobody would forbid aliasing
#send_to_elements) but about readability.

But maybe I am reading too much about Clojure lately ;).

>> Can you do this with lazy Enumerators?
>>
>> fibs = cons_stream( 0 ){ cons_stream( 1 ){ add_streams(fibs, fibs.tail) }
>> }
>
> I can't do it that compactly (though maybe someone can). Here's some
> doodling with the block form of an enumerator:
>
> fib = Enumerator.new do |y|
> # y is a "yielder" object -- lazy yielding via <<
>  y << 1
>
>  a,b = 0,1
>  loop do
>    y << a + b
>    a,b = b, a + b
>  end
> end
>
> p fib.next
> p fib.next
> p fib.next
> p fib.next
> p fib.next
>
> # Output:
> 1
> 1
> 2
> 3
> 5
>
> Or maybe something using cycle.

Wouldn't Kernel#cons_stream be great for this expressiveness? BTW it
does not necessarily mean that Enumerators should not be lazy, they
could be the foundation of the "functional" interface of streams as I
have of course a class hidden behind my "functional" implementation of
streams.

Cheers
Robert
-- 
Toutes les grandes personnes ont d’abord été des enfants, mais peu
d’entre elles s’en souviennent.

All adults have been children first, but not many remember.

[Antoine de Saint-Exupéry]