Purely stack-based generators

[Walter Bright]

Norbert Nemec wrote:
> Walter Bright wrote:
>> The trouble with a generator using the caller's stack is that then the 
>> generator cannot recursively call itself (such as if it was walking a 
>> tree). In order to work properly in the general case, a generator has 
>> to allocate all its local variables on the heap.
> 
> Which concept of generators do you refer to? The stack-based generators 
> that I suggested do in fact work recursively. A generator can obtain its 
> values from other generators or even recursively from itself without 
> needing heap space anywhere.

How can it do that, and yet allow the calling function also call other functions?