[Python-ideas] "While" suggestion

[David Borowitz]

Another good reference is the "as-if" rule in C. It's similar to operational
semantics, but may have enough denotational semantics semantics to be what
you're looking for. Don't know of a canonical reference, but Google is
useful:
http://docs.sun.com/app/docs/doc/819-5265/6n7c29d9f?l=ko&a=view

On Thu, Jul 31, 2008 at 20:00, Terry Reedy <tjreedy at udel.edu> wrote:

>
>
> David Borowitz wrote:
>
>> Precisely: you're talking about two different accepted definitions of
>> semantics:
>> http://en.wikipedia.org/wiki/Formal_semantics_of_programming_languages
>>
>> I'm not going to say one type of formal semantics is better than another,
>> but it's nice when everyone is at least on the same page :)
>>
>
> Thank you for the reference.  I see that denotational and operational are
> just the beginning of the semantics of semantics.
>
> In writing about and comparing algorithms, I need a term that is slightly
> in between but closer to operational than merely denotational.  I am
> thinking of using 'operationally equivalent' to describe two algorithms that
> are denotationally (functionally) identical and which compute the same
> essential intermediate objects (values) in the same order, while not being
> 'operationally identical' (which would make them the same thing).
>
> Wikipedia refers 'operational equivalence' to 'observational equivalence'.
>  Other hits from Google suggest that it have been used variably to mean
> things from operationally identical to merely denotationally (functionally
> identical), but therefore a complete substitute in the users operations.
>
> In the present case, we agree that [genexp] == list(genexp] in the Python
> meaning, denotational and operational, of '==', which is to compare the
> denotational meaning of two expressions (the resulting objects and their
> values).  I also claim a bit more: [genexp] could be but does not have to
> be, and in current CPython is not, operationally identical to list(genexp).
>  But I do expect that it is operationally equivalent in the sense above.
>  The essential objects and operations are the list contents and the list
> that starts empty and grows one reference at a time via append().
>
> Terry Jan Reedy
>
>
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-- 
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-Tom Stoppard

Borowitz
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