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Re: optional user-specified end-delimiters

This page is part of the web mail archives of SRFI 109 from before July 7th, 2015. The new archives for SRFI 109 contain all messages, not just those from before July 7th, 2015.

Per Bothner scripsit:

> It seems reasonable to allow an integer label, so we allow starting
> with a digit.  Thus for simplicity we also allow hyphen, underscore,
> or period.

I think starting with a digit is just an extra complication, and
we shouldn't have it.  It's a special case that needs to be tested,
documented, and learned separately.

> (In an unrelated change, I think tagname-subsequent should allow
> periods.  XML compatibility is one reason.)


> extended-string-literal ::= "&" string-starttag?
>    "{" initial-ignored? string-literal-part* "}!" string-endtag?
> string-starttag ::= "!" label
> string-endtag ::= "!" label
> The string-endtag is required if the string-starttag is specified,
> and of course the labels must match.

I think the string-endtag should be label followed by "!" instead.
That way all the content, including both labels, is between "!" and "!".

> Note this chance means that an extended-string-literal must be
> followed by a delimiter or end of input.
> For a named quasi-literal, we can use the constructor-name as an end-tag:
> &example{
>   &|line1
>   &|line2
> }example

I am very much against this, for reasons given earlier:  "}example" should not
be distinct from "} example", since "}" is a delimiter.

> You can add an explicit label:

I think an explicit label is the way to go.

> &example!23{
>   &|line1
>   &|line2
> }example!23

I'd change this to "}23!", modulo not allowing digit-strings.

> If may occasionally be useful to make labels available for
> semantic information.  One  example is as implicit "id" attributes.

I think that is a very bad mistake.  The labels should be purely syntactic
and discardable, like the numbers used in #2# and #2= datum labels; it's
all the same if you write #2=(a . #2#) or #333=(a . #333#), and the Lisp
system does not have to distinguish.

> There are some plausible alternatives.  For example we can put the
> end-tag just before the right brace.  For named constructors we
> could use:
> &cname{
> line1
> line2
> &cname}

That won't fly, because "&cname" is a perfectly cromulent substring.

I really dislike your other alternatives as well.

John Cowan   http://ccil.org/~cowan    cowan@xxxxxxxx
We want more school houses and less jails; more books and less arsenals;
more learning and less vice; more constant work and less crime; more
leisure and less greed; more justice and less revenge; in fact, more of
the opportunities to cultivate our better natures.  --Samuel Gompers