Re: Modula 2

[William Clodius <wclodius@lanl.gov>]

Robert A Duff wrote:
> <snip>
> Wirth's language descriptions are quite short, primarily because he
> tends to leave out a lot of important details, IMHO.  That's his style.
> I would expect a definition of any of Wirth's languages, suitable for
> standardization, would be much longer than Wirth's original, even if
> there were *no* extensions or use of VDM.
> <snip>

Yes it would be longer, but not fifteen to twenty times longer. Note for
example that ISO Pascal ISO 7185:1990 is 78 pages long, which is two to
three times the size of Wirth's original definition, and extended Pascal
is 214 pages long, about six to eight times the size of Wirth's original
definition after adding numerous extensions. (Yes I agree page count can
be misleading, but that is the main data I have at the moment.)

Wirth's Modula 2 was a more complicated than his Pascal, but not a lot
more complicated. A Modula 2 standard giving the main syntax and
semantics in 100-125 pages and additional libraries in 100-125
additional pages would have been viewed as a reasonable extension and
clarification.

To put it into other perspectives:

	The Modula 2 base language document is (in terms of page count) almost
40% larger than the Ada 95 standard, without providing object
orientation or generics. Including the separate later documents giving
these extensions results in a nominal definition well over 50% larger
than the Ada standard, but still less functional than Ada 95.

	The Modula 2 base language document is (in terms of page count) about
2% smaller than the C++ standard. The library is not nearly as
functional as that of C++.

	Algol 68's two level grammar, that provides precision comparable to the
VDM, was used to define a language of comparable complexity (excluding
libraries) in complete detail in, Robert Dewar will probably correct
this, I believe a little under 200 pages.

	The VDM specification has not fulfilled the role the committee espected
for it when standardization started. They hoped to be able use the VDM
as input to automatic tools to verify the self consistency of the
standard, but resource limitations kept the tools from being completed.
It has instead resulted in extra work that delayed publication and made
the standard more difficult to read for those unfamiliar with VDM (most
compiler writers and reviewers of the draft standard are unfamiliar with
VDM).

	The exception handling mechanism specified in the Modula 2 document is
very different from PL/I, Ada, or C++, and was widely viewed as an
unwise experiment for a language standard.

	The libraries as a whole were rather experimental and had little match
to those described by Wirth in his Modula 2 texts.

	Some "countries", e.g., Sweden, that did not file formal objections to
the standard, included comments to the effect that the standard when
adopted would kill the language.

-- 

William B. Clodius		Phone: (505)-665-9370
Los Alamos Nat. Lab., NIS-2     FAX: (505)-667-3815
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