Re: (For the Wikipedia article) Algorithms and format

On Sat, Nov 28, 2020 at 07:20:15PM +0100, Giovanni Piredda wrote:
> 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.

This is just to say that the parser of TeX is a complete programming
language on its own.  This means that it is undecidable whether
a given program is parsable.  TeX has no well-defined grammar,
contrary to *ML languages (HTML, SGML, MathML) or TeXmacs.
This is actually a very serious problem (it makes it impossible to
write 100% reliable convertes) and a genuinly stupid one,
because this problem is easy to avoid by design.

> 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.

See also The Jolly Writer, section 1.8.

> I am not going, at least for the moment, to write any comparison to
> LaTeX in the article on TeXmacs.

Sure, I also think that the page on TeXmacs is not the appropriate place for that.
I just mentioned it to make the similarities and differences clear.

> I have thought a bit on why LaTeX/TeX is so successful,

One of the keys is that it cannot easily be converted to something else.
Proprietary formats such as early M$ Word are another way to make this task hard.

> 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.

Easy in appearance.

If it is that easy, try writing a converter to some other format.

Best wishes, --Joris

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