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From: juul@diku.dk (Anders Juul Munch)
Newsgroups: comp.lang.ada,comp.lang.misc
Subject: Re: "Subtract C, add Ada"
Date: 26 Jan 1995 14:32:53 GMT
Organization: Department of Computer Science, U of Copenhagen
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Xref: pad-thai.cam.ov.com comp.lang.ada:14711 comp.lang.misc:6971
Date: 1995-01-26T14:32:53+00:00
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ncohen@watson.ibm.com (Norman H. Cohen) writes:

>I think CLU, circa 1979, still holds the prize for the best iteration
>abstraction.  When defining a CLU abstract data type that represents some
>sort of collection, you can define one or more iterators among its
>operations.  An iterator is like a procedure declared to take a value of
>the collection type as a parameter and to "yield" values of some element
>type.  The iterator is executed as a coroutine during the execution of
>the loop.  Values that are yielded by the iterator become the values of
>the loop parameter on successive iterations of the loop.

>My CLU syntax is rusty, but if you have the equivalent of a private type
>for doubly linked lists, you could define the following iterators for it: 

>   elements =
>      iter(l: list_type) yields (element_type)
>         next: cell_type = l;
>         while next.forward_link ~= l do
>            yield(next.item)
>         end
>      end

>Then you could iterate over the private type as follows: 

>   for item in elements(my_list) do
>      ...
>   end

>[lotsa stuff omitted]


Very nice.  But how about the kind of parallel iteration over two lists, 
that other posters showed for Sather and ICON.  Can you do that in CLU also?


-Anders Munch, juul@diku.dk
Still confused but at a higher level