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

[Giovanni Piredda]

On 28.11.20 22:57, TeXmacs wrote:
> 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)

So "possibility to write converters that work always" is one point that 
I am going to write in the Wiki page I think.

> > 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.


Thanks, here it will take a bit (the explanation on top helped).

> > 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.

Right. Once that you have many pages written in the format, it is 
difficult to switch to something different. This is also (perhaps) one 
of the reasons why the LaTeX code written by programs looks usually 
quite different from the one written by people---there are too many ways 
to do the same thing.

> > 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.

I meant "easy to read for me". This is subjective *and* only loosely 
related to how easy is to read it mechanically, i.e. with an 
algorithm---I saw this position that I am taking now only taken once by 
another person on the Internet, and a similar position ("reading TeX is 
second nature after a while", but without comparison to other markup) 
taken by other two persons (one in flesh and blood, one on the 
Internet). By the way I can read at sight only simple mathematical 
formulae written in TeX, but I do worse with all of the other markup 
systems I know.