NYCPHP Meetup

[James Wetterau]

"Tim Gales" says:
...
> > Another important practical distinction is that a high-level 
> > language is presumably portable between different computers. 
> 
> Who is doing the presuming in your view? 

I am, but I think this is not an uncommon view of a key advantage of
high-level languages.

> A language author creates a language to be useful.

At least in the case of C, a component of that usefulness was
portability across platforms, and I think today it is commonly
expected that portability across platforms is a key aspect of the
utility of high-level languages.  

Kernighan and Ritchie, the authors of C say about C in their classic
book "The C Programming Languages", 2nd ed., in the introduction:
"Although C matches the capabilities of many computers, it is
independent of any particular machine architecture.  With a little
care, it is easy to write portable programs, that is, programs that
can be run without change on a variety of hardware.  The standard
makes portability issues explicit, and prescribes a set of constants
that characterize the machine on which the program is run."

I think the last sentence pertinent to the ANSI standard is
particularly telling -- portability, which was implicit in the
language from very early on was made explicit in the standardization
process of the 70s - 80s. 

I am humbled to report, in the spirit of full disclosure, that the
text in the preface describes C as 'not a "very high level" language',
and the text in the introduction describes it thus: "C is a relatively
'low level' language."

So we seem to be in a semantic muddle.  Perhaps the correct
description would be: C is a standardized, portable relatively low
level language for a high level language which is not a very high
level language.

Maybe C would best be thought of as a middle level language; we could
call it a "mezzanine" language.

> If he/she is successful, i.e. the language proves to be 
> useful, other people port it to their systems so they 
> can also take advantage of it.

Or in the caes of K&R, I believe they did the first couple of ports
themselves.

> Maybe some authors of languages have a design goal of not 
> burning any bridges when it comes to portability -- since

In the case of K&R they were going for portability from early on so
that they could easily move this large program they had written called
"Unix" from one computer to another without having to rewrite huge
chunks of it ever time.

...
> different types of systems, but by and large computer languages 
> are created to get something done in one environment.

You may be right, but I don't believe that's the case with C/C++ and
Perl, to name just a few.

> Even Java, which now even runs on my cell phone, was designed to 
> run in a closed environment -- namely set top boxes.

Well, this is a simplification.  The first prototype of Java (called
"Oak") was meant to run on a variety of set-top boxes (to get ready
for the coming "digital convergence").  It was meant to be processor
independent but to present a consistent programming environment and
language.  Evidently a contingent at Sun expected that something that
would be sort of a hybrid between cable modems, web tv,
movies-on-demand, and TiVO, probably working over the internet, was
going to be the next big thing in 1991.  Not completely wrong, but not
exactly right.

...
> > The definition of a compiler or interpreter or virtual 
> > machine includes the ability to read source code in a 
> > high-level language and generate correct executable programs 
> > for different kinds of computers.
> > 
> 
> No, I don't think portability has anything to do 
> with being a high-level language.

Well, I think it's a commonly associated feature, and a non-portable
high-level language would be a gross exception.  I suppose a vehicle
doesn't have to have seats to be a car, and I don't know if the
definition of "car" should include the idea that there are seats in
it, but it seems to me to be the convention.  Similarly, I think
portability is a commonly expected advantage to high level languages.

Of course none of this applies to C, since we have established, from
the words of its creators, that it is a mezzanine language.