On 26 Apr., 21:15, Scott Moore <sam...@[EMAIL PROTECTED]
> wrote:
> thomas.mer...@[EMAIL PROTECTED]
wrote:
>
> > Pascal 6000 which predates P4 already had an 'otherwise'
> > clause. IMHO it was a big mistake to omit it in the P4
> > compiler and in the ISO 7185 standard. Do you plan to
> > add 'otherwise'/'else' to the P5? Since I switched
> > from Pascal to C in the early 90s, I am not sure if
> > modern Pascals prefer 'otherwise' or 'else' for 'case'
> > statements.
>
> Yes, it was (the otherwise) an extension that was local
> to the University of Minnesota version.
>
> Remember that the P4 compiler was designed in the 1970's
> by Wirth's students in Zurich, and was not designed to implement
> the entire Pascal language as it existed at that time, it was
> deliberately subsetted.
>
> I have considered P4 to be a historical item. There are actually
> a lot of copies running around the net, as you have seen in
> this thread (Steve pemberton has a copy, so does the CDC 6000
> history group). I updated it to be ->source<- compliant with
> ISO 7185 because otherwise, I wouldn't be able to compile it,
> since I don't use a CDC compiler from the 1970s (even the 1984
> CDC 6000 compiler would have refused to compile it in the
> original form).
In the middle of the 80s a friend an I copied the P4 from the Book
"Pascal Implementation" from S.Pemberton / M.C.Daniels. We used a
CDC Cyber and therefore we only used upper case characters. Our
p4.pas was identical to the book. Our p4r4.pas had the changes
necessary to compile it with the Pascal-6000 Compiler. Later I
created also a p4t.pas for Turbo Pascal. Recently I created a
p4g.pas which can be compiled with the gpc. All of them are written
in upper case characters. An attempt to use the P4 as basis for a
Seed7 compiler at the beginning of the 90s failed (at that time I
did not use the name Seed7). The development of the current Seed7
interpreter (hi) started as Pascal program with no relation****p to
the P4. Later I switched to C. So the current Seed7 implementation
does not use Pascal.
For Pascal programmers Seed7 programs will look very familiar.
Seed7 tries to take over some of the Pascal philosophy.
> Of course it would be useful to also have
> a more modern, updated P4, which I did, and called it P5.
>
> Now, lets go over my plans for P5 (and beyond), then lets
> go over yours :-)
>
> 1. P5 was P4 brought up to accept ISO 7185 as well as to be
> written in ISO 7185. Basically ISO 7185 is the 1970's Pascal,
> with clarifications made by the Pascal standards committees.
> It is P4 with the "subsetting" removed.
>
> 2. I agree that P5 should go further, such as extended
> constructs. I would tend to call that P6 or more (p7, p8, etc).
> Of course, its according to time permitting.
>
> How about your plans? Its really up to you if you want to go
> to town adding new constructs. That's what Wirth wanted when
> he (they) issued the P4 kit.
>
> So I would say, if you want an otherwise clause, that would
> be a good starting place for you to get used to
> changing/extending the compiler!
At this place I should explain my plans.
I started to rewrite the P4 in Seed7. The reason I do this, is to
show what can be done with Seed7. There are also other Seed7 example
programs like a Basic interpreter and other stuff. The Seed7 version
of the P4 is already capable to compile the original P4. The
resulting P-Code is identical to the one that the GPC version of the
P4 creates when the original P4 is compiled. There are still things
to be done, so it will take some time unil I can release the p4.sd7.
An improved version of p4.sd7 could be called p7.sd7 (A name which I
plan to use to reflect that it is a P4 written in Seed7). Such an
improved p7.sd7 could sup****t ISO 7185 and other extensions like
'otherwise' clauses. Since I use most of my energy/time to improve
Seed7 I am interested to reuse your impovements of the P4. I asked
for the GPL because I release all my code under the GPL (and the
LGPL for libraries).
> Remember that Steve Pembertons description of the P4 compiler
> is online, and so are other original documents on it written
> back in the 1970s (see the
> http://www.standardpascal.org/documents.htmlsection
on the
> website).
>
> P5 adds new SC (Stack Computer) operation codes, but the changes
> are well documented in the source, so the P4 documentation plus
> the source will be adequate. I also hope to produce more
> sup****ting documents for the P5 compiler in the near future.
I look forward for that.
> > BTW.: Under which license is the P5 released?
> > GPL would be great.
> > Would there be a conflict the public domain P4 and the GPL?
>
> > Greetings Thomas Mertes
>
> I don't see any. Public domain is a centuries old concept, and
> the P4 compiler has been public domain since the 1970s (since
> it was created).
>
> Of course, it is debatable what GPLing a public domain software
> means, since anyone can take the old, public domain version of
> the P4 compiler and do whatever they want with it, without
> regard to the GPL.
>
> It seems to me that what you would be effectively doing by
> taking a P4 or P5 compiler, changing it and GPLing that, would
> be that nobody could use your version of the compiler without
> obeying the GPL.
Since I release all my programs under the GPL this is okay for me.
Greetings Thomas Mertes
Seed7 Homepage: http://seed7.sourceforge.net
Seed7 - The extensible programming language: User defined statements
and operators, abstract data types, templates without special
syntax, OO with interfaces and multiple dispatch, statically typed,
interpreted or compiled, ****table, runs under linux/unix/windows.
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