At 07:55 2009-08-13, Bob Calco <[email protected]> wrote:
> >
> > Ted Roche wrote:
> > > On Wed, Aug 12, 2009 at 6:36 PM, Gene Wirchenko<[email protected]>
> > wrote:
> > >
> > >> At 08:38 2009-08-11, Alan Bourke <[email protected]> wrote:
> > >>
> > >>> Mea culpa, but not language as in 'programming language'!
> > >> How would you differentiate the two?
> > >>
> > >> Fair warning: I am taking a course in the theory of
> > computation.
> > > Well, then, you really ought to know already, shouldn't you? :)
> > >
> > > I'd take a swipe at it: a markup language (XML, HTML) is a syntax and
> > > grammar for describing the metadata that dictates the structure and
> > > representation of data. optionally contained in a document. In
> > > contrast, a programming language provides instructions for an
> > > interpreter/compiler to execute against said data.
> > >
> > Or maybe : a markup describes a desired result whereas a programming
> > language describes a series of actions (though that would put SQL into
> > the markup camp).
>
>The issue is the number of layers of separation from the physical
>computational paradigm of the machine to the logical constructs of the
>human-readable language.
One can arbitrarily add layers. For example, a CPU implemented
in microcode add one more layer. There are even systems with more
than one layer of microcode: nanocode and, I think, picocode also exist.
>Some languages are low-level, and operate more or less along the same
>logical paradigm as the machine's physical structure---that is, they are
>stack based, with registers, a heap, etc., all of which you have explicit
>access to in terms of language constructs. C/C++ are in this category, as
>well as most native-compiling imperative languages (Delphi, D, Ada, etc).
C does not have stacks. C runs on systems that do not have
stacks. Do you consider stacks to be at the same layer as other
instructions? They are an abstraction on some systems.
>You feed logical instructions to the computer according to a dialect of the
>computer's physical memory model, one at a time, each one having a fairly
>direct translation to the underlying assembly -- which is itself a
>"language" describing with one-for-one mnemonics what is to happen in the
>machine. The concept of the data being separate from the instructions at
>this level is pedantic to the point of irrelevance: Instructions always
>operate on, or with, or in relation to real data, located somewhere in
>memory.
Instructions operate on data even if the data is instructions.
>Higher level languages tend to me more declarative and functional, trusting
>the compiler (or interpreter) to handle the lower level mapping of language
>concepts to computer instructions. Higher level languages, especially pure
>functional languages like Haskell, actually put less focus on both the data
>and the instructions and more focus on the logic. It's the mid-level, OO
>languages that actually are data-vs.-instructions-obsessed.
>
>XML could be considered a language, if a compiler translates (or even
>interprets) the "code" to actions executed in the computer. Eg, XSLT, which
>actually has a limited but Turing-complete number of control primitives,
>does indeed "execute" a transformation from an XML source to something else
>(another XML file, a PDF, an HTML file, etc.). Or it might just be a generic
>markup describing data. I've used it for code generation, i.e.,
>metaprogramming, a lot on several different programming platforms. I tend to
>think of it as a meta-language when obvious comparisons to cholesterol or
>snake oil aren't foremost in my mind. :)
Which is when? <EG>
>XML has been in search of what it really is since it's "discovery". ;)
I agree.
Sincerely,
Gene Wirchenko
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