Re: Generators/coroutines in future Ada?

[Victor Porton <porton@narod.ru>]

J-P. Rosen wrote:

> Le 12/07/2017 à 01:19, Victor Porton a écrit :
>> Dmitry A. Kazakov wrote:
>>> I don't understand what is wrong with:
>>>
>>>     type Stateful is limited private;
>>>     function Generate (X : not null access Stateful) return Things;
>> 
>> The thing "wrong" with this, is that it is sometimes hard to implement
>> Generate(). In Python this can be done in an easier way by using
>> generators (Python's "yield" keywords).
>> 
> Please provide a concrete example, so we can compare solutions!

I don't have at hand an Ada example. So instead I will give two examples in 
Python with and without explicit generators. Which of the two is simpler?

   1 # Using an explicit generator function
   2 def firstn(n):
   3     num, nums = 0, []
   4     while num < n:
   5         yield num
   6         num += 1

and

   1 # Using the generator pattern (an iterable)
   2 class firstn(object):
   3     def __init__(self, n):
   4         self.n = n
   5         self.num, self.nums = 0, []
   6 
   7     def __iter__(self):
   8         return self
   9 
  10     # Python 3 compatibility
  11     def __next__(self):
  12         return self.next()
  13 
  14     def next(self):
  15         if self.num < self.n:
  16             cur, self.num = self.num, self.num+1
  17             return cur
  18         else:
  19             raise StopIteration()

Modified from
https://wiki.python.org/moin/Generators

-- 
Victor Porton - http://portonvictor.org