[plt-scheme] generators with sequences

Robby Findler wrote:
> One other thought: did your explorations with the call/cc variant
> suggest ways that Ruby might be broken? Did you try to confirm that?
> It may shed some light on the Scheme version.
>
>   
Initially I was inspired by python but I tested Ruby and Python and 
found them both to be ok. It doesn't seem possible in either language to 
capture a generator's yield function and call it in a separate place. Of 
course this also means you can't call yield from a helper function and 
have it do what you expect (pointed out to me by a few people).