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Re: [Texmacs-dev] (For the Wikipedia article) Algorithms and format

From: Giovanni Piredda
Subject: Re: [Texmacs-dev] (For the Wikipedia article) Algorithms and format
Date: Sat, 28 Nov 2020 19:20:15 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0

On 28.11.20 18:21, TeXmacs wrote:
Hi Giovanni,

On Sat, Nov 28, 2020 at 05:58:07PM +0100, Giovanni Piredda wrote:
I have a few questions, I am going to use the answers to improve the
Wikipedia article
Thanks; that is very useful indeed.

Maybe you could also look at the translations in various languages.
With Google translate, you should be able to get at least very basic info right.
I noticed that some of the Wikipedia pages are hopelessly outdated.
For instance, the French page is not aware of the existence of a Windows 

I will try and see what I can do. I can read some of the languages, but I am unable to write in them.

But perhaps it is sufficient to substitute the current information for the outdated (or copy a part of a sentence, substituting in the "values"), in which case I will be able to do it.

I am first writing in the English version, then modelling the Italian one after it. Maybe a small section on the history of interactive editing of structured text will be nice; I do not know if I will be able to write one (I have collected some literature), for the moment I have added one sentence at the beginning.

I find Lilac, a program from the end of the 80s, with its two view editor, an interesting software. One can find online a document which is a slightly edited version of the PhD thesis of Kenneth P. Brooks "A Two-view document editor with user-definable document structure" (one copy on bitsavers.org, the other one at https://www.hpl.hp.com/techreports/Compaq-DEC/SRC-RR-33.pdf, hpl is a web site of hp, the downloads look if not legal, at least reasonable, as they are the only way to read the document). I read a few pages and it looks like he addressed some of the issues that also TeXmacs addresses; I am generalizing from the only example that I have in mind---Sec. 2.4, pag 13, Mapping: "When the user points and clicks to make a selection, Lilac must figure out what object in the document he is pointing to. ... we need to perform a mapping from positions on the screen to nodes in the program's syntax tree".

Said this:

1) Which algorithm does TeXmacs use for line-breaking?
It is called "global" line-breaking, i.e. the algorithm takes into
account the whole paragraph to be rendered and optimizes the line breaks
globally for the whole paragraph.  This as opposed to "first-fit"
line-breaking, which simply finds the best line break for
every next line in succession.

So it is not the same algorithm as Knuth-Plass, but it follows the same spirit.

2) Is the algorithm for page-breaking unique to TeXmacs? If not,
what is it? Maybe the extension of the one for line-breaking?
TeXmacs uses a global algorithm for page-breaking,
which is extremely complex, because it also deals with
floating objects (figures, tables, footnotes, etc.) and
multi-column content.

Thanks for this information, this belongs in Wikipedia.

LaTeX cannot do this.

3) Is the TeXmacs format a form of SGML? Regardless of whether it
is, or it is not: how does it relate to SGML?
It is not SGML, but it is similar, with a well-defined syntax.

LaTeX has no well-defined syntax.  The grammar is Turing complete.

I will find a way to write this. Maybe you can correct later, after it is online.

I have in mind that the "Turing complete" expression describes a system of manipulation of symbols (I helped now myself with Wikipedia for finding the word "manipulation" in this context), by which starting with a set of symbols and applying the manipulation rules I obtain another set of symbols.

While I see a grammar as a set of rules that determine allowable compositions of symbols, but they do not tell how to compose any set of symbols.

But you wrote that the grammar is Turing complete. Could you explain more? Maybe a pointer to something to read, if it is to long to write here.

Finally for this message.

I am not going, at least for the moment, to write any comparison to LaTeX in the article on TeXmacs. I have thought a bit on why LaTeX/TeX is so successful, but I have a faint grip on the issues and I have very little data available (opinions expressed by people in person or read on the Internet). From the success of LaTeX we can I think deduce that having a syntax that satisfies the concept of "well-definedness" is not a necessary condition for widespread use ;-) although perhaps it places limitations that one could put into evidence.

The "markup" of TeX (I call it that way even if it is not markup) for me is the easiest to read among all of the markup languages I have seen (for mathematics especially, for other things too). Perhaps this has been also one factor for success.

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