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Re: RE: The remarkable similarities between XSLT and Flex/Lex

• From: Marcus Reichardt <u123724@gmail.com>
• To: Roger L Costello <costello@mitre.org>
• Date: Sun, 26 Jun 2022 18:52:44 +0200

> Am 26.06.2022 um 15:01 schrieb Roger L Costello <costello@mitre.org>:
> 
> There was also a strange
> unnecessary constraint on these expressions called "ambiguity", which
> *everybody* who wrote SGML software needed to understand, and so the idea of
> applying formal language techniques to SGML was inevitable.

Hmm, your anonymous source should've expanded on that; without proof or anything the claim of "unnecessary-ness" is void.

SGML has tag inference (can infer arbitrarily many start- and end-element tags) and moreover can expand short reference delimiters (arbitrary tokens not used a markup delimiters, including newlines and tabs/spaces) by context-dependendant replacement text (start- and end-elements typically). Determinism in content models helps a lot to make this even work, and as I hear, the same thing is being re-introduced as "Invisible XML", giving you a facility that was already there in 1986 ;)

Of course, with XML-style fully tagged markup, more relaxed models could be used, hence RelaxNG.

What is the argument here? That a Thompson construction for finite automata (as opposed to Glushkov/Antimirov derivatives) is more convenient for programmers since an off-the-shelve regexp lib can be used? Also, I don't quite understand the leap to pattern matching in XSLT; the only connection I can see is that in the early 2000s there were attempts to statically verify/type-check eg XPath expressions (over elements) ie decide whether those could yield non-empty results in the presence of DTD content model constraints. To the best of my knowledge, the results weren't convincing.

Best,
Marcus Reichardt
sgml.io

• References:
  • RE: The remarkable similarities between XSLT and Flex/Lex
    • From: Roger L Costello <costello@mitre.org>