Re: [xml-dev] How does XML limit "the range of implementationdecisions t

[Michael Kay <mike@saxonica.com>]

Well yes, the code we write generally ends up being executed on a von Neumann machine, and von Neumann machines are procedural, but that's not really the point. We're talking about the code we write, not the machinery for executing it.

Michael Kay
Saxonica

> On 23 Jun 2022, at 22:09, Stephen D Green <stephengreenubl@gmail.com> wrote:
> 
> The SQL is declarative, and non-procedural, but isn't the execution
> plan into which the SQL is converted, procedural? Isn't all
> declarative, 'non-procedural' code usually actually turned into
> something procedural behind the scenes? Isn't declarative,
> 'non-procedural' code actually an illusion, wrapping procedural code
> under the hood - smoke and mirrors? I might use a lambda LINQ
> expression to handle SQL databases or XML and think these are
> declarative or functional expressions which get computed, yet I'd be
> surprised if it doesn't actually get turned into a lot of procedural
> code that gets executed.
> ----
> Stephen D Green
> 
> On Thu, 23 Jun 2022 at 12:16, Michael Kay <mike@saxonica.com> wrote:
>> 
>> The domain he's referring to is not XML, but what he calls "scanning" (probably meaning here lexical analysis).
>> 
>> I actually think he's wrong. Nonprocedural programming is most successful in domains such as database query (SQL) where there's a vast range of implementation decisions to be made (query execution plans), and choosing the right one is best done by a machine rather than a human.
>> 
>> Michael Kay
>> Saxonica
>> 
>>> On 23 Jun 2022, at 11:45, Roger L Costello <costello@mitre.org> wrote:
>>> 
>>> Hi Folks,
>>> 
>>> A book [1] that I am reading says something interesting about declarative languages (such as XML):
>>> 
>>> Programming a scanner generator is an example of nonprocedural programming [i.e., declarative programming]. That is, unlike ordinary programming, which we call procedural, we do not tell a scanner generator "how" to scan but simply "what" we want scanned. This is a higher-level approach and in many ways a more natural one. ... Nonprocedural programming is most successful in limited domains, such as scanning, where the range of implementation decisions that must be automatically made is limited.
>>> 
>>> That last sentence is interesting. I wonder how it applies to XML? XML is in a limited domain, right? XML's domain is the data formats domain, right? How is "the range of implementation decisions that must be automatically made" limited in XML?
>>> 
>>> /Roger
>>> 
>>> [1] "Crafting a Compiler with C" by Fischer and LeBlanc, p. 52
>>> 
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>> 
>> 
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