How does `xii.tex` work? - TeX

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How does `xii.tex` work?

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निरंजन

I recently came to know about David Carlisle's package [`xii`](http://ctan.org/pkg/xii). The code and the output look SO different from each other that I am curious to know the meaning of that code. Can anybody explain how that code works?

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Phelype Oleinik replying to barbara beeton

That's impressive, indeed!  David wrote the code very carefully to need only a single `%` for a line termination.  My first attempt at a square of code required almost all lines terminated with `%`

barbara beeton replying to Phelype Oleinik

But you've not mentioned the crowning touch -- the fact that the code is neatly packaged into a perfect rectangle.  That' what boggles *my* mind

barbara beeton replying to निरंजन

If you understand Latin better than you understand English, there's also xii-lat based on the same approach.

निरंजन replying to Phelype Oleinik

May be I'll start my journey in TeX with this :)

Phelype Oleinik replying to निरंजन

Once I dissected that code (maybe I have the dissected version somewhere). It's not _hard_ to understand, but it takes a bit of patience.  There are two main parts that add to the complication:  first is the obfuscation with catcode changes (making single letters behave as macros), and then the text compression.  The text is written such that roughly only the last verse is written in full, and the last ones are build from that step-by-step.

निरंजन

@samcarter @Joseph Thanks for the references. I'll read them.

Joseph Wright

https://tex.stackexchange.com/questions/105808/how-could-the-macro-xii-tex-be-simplified-into-a-better-readable-form covers this, more or less

samcarter

A step-by-step walk through:  
https://groups.google.com/g/fr.comp.text.tex/c/tkyaRYXQWnQ/m/wY_0x8lX1KoJ  
(unfortunately only in  French)

samcarter

One of the methods uses is changing the catcodes, e.g. have some other letter act like the `\` in normal tex code and suddenly you don't recognize macros any more.

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