Walter: any plan to add support for yield/return Iterators/generators?

[Marcio]

	Indeed a single stack can be used if you impose limitations. See what 
Barbara Liskov says in "A History of CLU":

http://www.lcs.mit.edu/publications/pubs/pdf/MIT-LCS-TR-561.pdf#search=%22A%20History%20of%20CLU%22

3.10. Iterators
"Iterators are related to coroutines; the iterator and the body of the 
for loop pass control back and forth.
However, their use is limited so that CLU programs can make do with a 
single stack."
[...]
"Imposing the limitations on iterators was done to get the efficient, 
single stack
implementation, albeit at the expense of some expressive power."

And she credits the original invention to Alphard:
[Shaw, 1977]
Shaw, Mary, William Wulf, and Ralph London, Abstraction and Verification 
in Alphard: Defining and Specifying Iteration and Generators, 
Communications of the ACM, 20:8, August 1977.

marcio

Marcio wrote:
>     I was saying a functor would be a smalltalk block. But I still 
> inquire if that is really enough for generators, and I am not sure. So, 
> we are not disagreeing (you and me). Maybe we are disagreeing with 
> Walter's claim that just a functor is enough.
> 
>     Having said that...
> 
>  > For each instance of a generator, you need a complete separate stack.
>  > That stack is kept on the heap, separate from the normal processor
>  > stack. Both have to be full stacks, since both contexts need to
>  > support function calls - even recursion - independently. Even though
>  > the generator itself is likely to be a single function with yields
>  > done directly from itself, it still needs to call normal functions to
>  > do its stuff.
>  >
> 
>     ... Perhaps the caller will see its runtime stack used by the 
> generator as it runs until its next yield/return. So, the environments 
> are maintained in the heap and survive the return (therefore values of 
> variables are remembered) while the stack used between 2 yield/returns 
> is borrowed from the caller's stack. So, in this case Walter would be 
> right.