Re: Delimiters for pragmas

Steven Pemberton <steven.pemberton@cwi.nl> writes:
> One way to combat that is to make it clear that pragmas have no effect
> on the language: by making them a subset of comments, it is a clear
> message that there can be no substantive effect,

I can see, and I’m sympathetic to, this argument on psychological
grounds, but it can’t be made on technical grounds. Let’s take John’s
hypothetical example of a “fred” comment to the processor that has the
effect of making the grammar insensitive to case within a given rule.

If my processor is willing to implement this behavior then the syntax
doesn’t matter. If ixml has a pragma syntax, that’s what I’ll implement:

[fred] rule: productname, value.

if it has a standard mechanism for identifying “implementation
comments”, that’s what I’ll implement:

{[fred]} rule: productname, value.

and if it has nothing, I’ll invent my own hack in comments (if I don’t
just extend the grammar), and that’s what I’ll implement:

{#fred} rule: productname, value.

> because removing comments can have no effect on the language.

Removing that comment *will* have an effect on the language in my
implementation. Saying it’s in a comment will not, can not, and does not
change that.

Likewise, saying that my processor is non-conformant in this case, which
might very well be true, has no more or less (technical) force than
saying a pragma that implements this behavior is requiring the processor
to behave in a nonconformant way.

> Making pragmas something different where the only intended audience is
> implementations, and each implementation can do its thing runs the
> risk of implementations using it as a playground for ixml divergence,
> and as a place where implementations can satisfy use cases without
> making them a standardised part of the language.

I can see how one form invites play and the other simply cannot forbid
it. I’m not entirely persuaded, but I also take your point about
committees doing design and how long that takes. If 

  {[implementation comment]}

Is the best we can do under the current constraints, I think I can live
with that.

                                        Be seeing you,
                                          norm

--
Norm Tovey-Walsh
Saxonica