Re: VMS Pascal article

On 1/3/2025 1:17 PM, Dan Cross wrote:

In article <67781447$0$711$14726298@news.sunsite.dk>,
Arne Vajhøj  <arne@vajhoej.dk> wrote:

On 1/3/2025 10:11 AM, Dan Cross wrote:

`readln` and `fgets` are not similar in that `readln` strips the
line ending sequence, and `fgets` does not.

>
Close enough for the purpose of this article.

 Perhaps.  I may be worth an asterisk, as often C programmers
will want to write:
      while ((s = fgets(s, len, fp)) != NULL) {
         char *nl = strchr(s, '\n');
         if (nl != NULL)
             *nl = '\0';
     }
 Which is a bit more cumbersome than the Pascal equivalent.  When
carriage returns get mixed in, it gets even nastier, so much so
that one may just write a helper function to deal with it.

I think you are right. I have added a note.

`f = fopen,fnm "r");` is an obvious typo.
`while not eof(f)) do` is an obvious typo.

>
Fixed.

 Fixed, but the comparison to C is slightly wrong:
 `while not(eof(f)) do` is not exactly the same as
`while(!feof(f))`.  In particular, while in VSI Pascal `EOF(f)`
will be true on the first iteration of the loop if `f` is empty,
the same is not true for `feof` from stdio: in order for `feof`
to be true, stdio must observe the end-of-file condition of `f`
via some input operation.  This leads to awkward code sequences
like this:
      ch = fgetc(fp);
     while (!feof(fp)) {
         /*
          * Do something with `ch`
          * ...
          */
         ch = fgetc(fp);
     }

C feof is a crap function.
I think I will drop feof completely and add fgetc
not returning EOF. I already have fgets not returning NULL.

The structure you present at the end as "equivalent" of a
varying character array is not correct.  `integer16` is a signed
type, with a maximum value of 32,767.  The length field for a
`varying [n] of char` is an integer subrange type with word
representation.  That is, `length` is unsigned 0..max, where max
is <= 65,535.

>
Ooops.
>
You are right.
>
I was sure that the limit was 32K but it is 64K.
>
Fixed.
>
And also fixed in the description of VARYING further up.

 You should seriously mention the STRING type, though.

I think VARYING OF CHAR is what is used most in VMS Pascal.

Also, it's a bit of a bummer that you didn't mention nested
functions/procedures, which are among the cooler aspects of the
language:
 $ type foo.pas
(* foo *)
program foo(output);
procedure hello;
     procedure world(var who: String);
         function punct: char;
         begin
             punct := '!'
         end;
     begin
         who := 'World' + punct
     end;
var
     who: String (10);
begin
     world(who);
     writeln('Hello, ', who)
end;
begin
     hello
end.

There is already an example. fac is inside testfac.
I will add a note about it.
Arne