[texhax] help with programming LaTeX

[Karl Berry]

    I need some tutorial or some book on programming LaTeX. 

http://www.latex-project.org/guides/clsguide.pdf has some stuff,
although it doesn't start from zero.

FAQ entry with more links:
http://www.tex.ac.uk/cgi-bin/texfaq2html?label=writecls

    how do I do a conditional loop? 

I don't know if LaTeX has special commands for loops.  In plain TeX,
you say
\loop
  foo
\if...
  bar
\repeat

where the \if... is any TeX conditional.  To nest loops, use groups.

There are some fancier packages that do fancier things, but that's the
basic idea.

There are plenty of books and guides on plain TeX, for example,
http://www.eijkhout.net/tbt/
http://tug.org/ftp/tex/impatient/

Hope this helps,
Karl