[Tex/LaTex] Parsing and programming in TikZ

parsingpgfkeysprogrammingtikz-pgf

Background: I'be been reading the PGF manual (keys section) and today the TeX Book just arrived in the mail and just started reading chapter 7 (How TeX reads what you type) — feeling like Mickey Mouse in "The Sorcerers Apprentice".

I want (but this is not the question) to do a routine that does something like that:

   input:   a,b ; c,d ; e,f.
   output:  a\nodepart{b} && c\nodepart{d} && e\nodepart{f}\\

My idea was to use the PGF parser to read the input. If I were using the languages I know (old Basic, Python, Maple script) I would save intermediary results in a variable but for what I understood so far LaTeX/TeX/ and TikZ/PGF do not work in this way. There is no string manipulation routines. I know we can store stuff into pgf keys. Before you stop reading I better ask my questions:

Are there any examples of (LaTeX/TeX/ and TikZ/PGF) code that reads some input of variable lenght possibly more than ten and spits some other code?
With the example above in mind, which references should I read to be able to implement the routine in an efficient way?

Post-script:

Reading the suggested tags, I just learn about the LaTeX parse package, will check it also.
@egreg: The ultimate goal will be to define a bimatrix environment in TikZ to display two-player games in normal form. The idea is to create outputs similar to this http://www.maths.lse.ac.uk/Personal/stengel/bimatrixgame/example.pdf but with the intuitive and human-like language we see in TikZ constructs.

Best Answer

This is an adaptation of the second answer of the question How do I split a string? to your problem. It is not exactly what you want, but it can help to get you on the way.

\documentclass[a4paper]{article}
\makeatletter
\def\processArg#1,#2{%
  #1 nodepart #2
}
\def\myutil@empty{}
\def\severalparts#1;#2\@nil{%
 \def\NextArg{#2}%
 \processArg#1%
 \ifx\myutil@empty\NextArg
     \let\next\@gobble
 \else XX
 \fi
 \next#2\@nil
}%
\def\ProcessString#1{%
   \let\next\severalparts
   \next#1;\@nil %
}%
\makeatother

\begin{document}
\ProcessString{a,b;c,d;e,f}
\end{document}

This the pdf output:

Result

Related Solutions

[Tex/LaTex] Programming simple functions using TikZ arithmetic

Thanks all for the comments, and Altermundus for your alternative answer. However, I really think that for users that would like to enjoy a higher level of abstraction (as opposed to low-level macro hackery) a much better interface for defining such simple functions could be implemented. We don't really have to go down to low-level TeX coding.

For the moment I'll forget about the issue with variable namespaces, but with your help and some tinkering with macros, reading the TikZ sources and lots of trial and error, I was already able to provide something much closer to what I'm looking for.

\documentclass{article}
\usepackage{tikz}
\usepackage{etoolbox} % for \ifdefstring

\makeatletter
\newcommand{\setmath}[2]{\pgfmathparse{#2}\edef#1{\pgfmathresult}}
\newcommand{\domath}[1]{\pgfmathparse{#1}\pgfmathresult}
\newcommand{\ifmath}[1]{\pgfmathparse{equal(#1,0)}\ifdefstring\pgfmathresult{0}}
\newcommand{\whilemath}[2]{\ifmath{#1}{#2\whilemath{#1}{#2}}{}}
\newcommand{\returnmath}[1]{\pgfmathparse{#1}\pgfmath@smuggleone\pgfmathresult}
\newcommand{\newmathfunction}[3]{\pgfmathdeclarefunction{#1}{#2}{\begingroup#3\endgroup}}
\makeatother

\newmathfunction{mygcd}{2}{%
  \setmath\a{#1}%
  \setmath\b{#2}%
  \whilemath{\b}{%
    \setmath\t{\b}%
    \setmath\b{mod(\a,\b)}%
    \setmath\a{\t}%
  }%
  \returnmath{int(\a)}%
}

\begin{document}
\setmath\a{15}
\setmath\b{6}
gcd(\a,\b) = \domath{mygcd(\a,\b)}.
\end{document}

Now you can actually read the code to compute the gcd, which was pretty much translated line by line from my original pseudocode. I know that this might be grossly inefficient but, who cares, I just want to compute the coordinates for a few points, I'm not trying to do sophisticated physics simulations here.

I would greatly appreciate any comments and suggestions to the programming interface that I propose; in particular using etoolbox just to compare against the token 0 seems like an overkill, but etoolbox was something that I could also easily learn.

[Tex/LaTex] Parsing hexadecimal numbers to binary and iterating over bits

The following is less impressive than the other answers from the visual point of view (Mark, I like yours!), but addresses the actual question of the OP: Bit-wise iteration over hexadecimal values, which becomes fairly easy when using the bitset package by Heiko Oberdiek:

\documentclass{article}
\usepackage{bitset}
\usepackage{pgf,pgffor}

\begin{document}

  \bitsetSetHex{mybitset}{AA}
  % use \bitsetGetSetBitList
  % expand first
  \edef\mybits{\bitsetGetSetBitList{mybitset}}
  \noindent
  \foreach \bit in \mybits {%
    Bit \bit{} is set! \\ 
  }

  % just itereate all bits
  \noindent
  \foreach \i in {0,...,7} {%
    Bit \i: \bitsetGet{mybitset}{\i} \\
  }

\end{document}

enter image description here

Best Answer

Related Solutions

[Tex/LaTex] Programming simple functions using TikZ arithmetic

[Tex/LaTex] Parsing hexadecimal numbers to binary and iterating over bits

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