Macro for a code translator

Question

Is there an existing macro that "translate" tokens using some code ? For example :

\def\code{{{a,b},{b,c},{c,a}}}
\translate[\code]{caac} % => would typeset "abba"

or even better something like that :

\def\code{{{ab,ba},{ac,ca},{b,c}{c,b}}}
\translate[\code]{abbcac} % => would typeset "bacbca"

The syntax for the code definition is not important.

If there is no such macro, any proposition is welcomed to obtain an efficient solution to this problem.

Thank you :)

What I have seen is using etoolbox to replace certain tokens in a macro. — bodo, Jul 19 '12 at 16:17
This is probably doable with regular expressions. See http://tex.stackexchange.com/questions/4347/regular-expressions-with-pdftex for a starting point. There are also regex questions and answers on stackoverflow. Regular expressions have a steep learning curve leading to a big payoff. — Ethan Bolker, Jul 19 '12 at 16:45
In fact, we need some kind of parsing strategy. Regexp can be used for such a thing but are not useful for doing the parse itself... — Xoff, Jul 20 '12 at 05:48

score 6 · Answer 1 · answered Jul 19 '12 at 16:28

6

A reasonably efficient implementation of the first one is

\def\translate[#1]#2{{%
\expandafter\xlc#1\relax
\lowercase{#2}}}

\def\xlc#1{%
 \ifx\relax#1\else
 \xxlc#1%
 \expandafter
 \xlc
 \fi}

\def\xxlc#1,#2{\lccode`#1=`#2 }

\def\code{{a,b}{b,c}{c,a}}

\translate[\code]{caac}


\bye

which typesets abba if run through plain TeX.

answered Jul 19 '12 at 16:28

David Carlisle

757,742

This is not as general as I hoped, but it's very nice to use the lowercase macro to achieve the goal, I like it :) – Xoff Jul 19 '12 at 16:45

Paul Gaborit · Accepted Answer · 2012-07-20T06:35:06.283

(edit: first parser of my initial answer was not using the right rules.)

Here's a TikZ/PGF solution:

\documentclass{standalone}
\usepackage{pgf}
\usepgfmodule{parser}

\pgfparserdef{myparser}{initial}{the letter a}{b}
\pgfparserdef{myparser}{initial}{the letter b}{c}
\pgfparserdef{myparser}{initial}{the letter c}{a}
\pgfparserdef{myparser}{initial}{the character ;}{\pgfparserswitch{final}}


\pgfparserdef{myparser2}{initial}{the letter a}{\pgfparserswitch{s2}}
\pgfparserdef{myparser2}{s2}{the letter b}{ba\pgfparserswitch{initial}}
\pgfparserdef{myparser2}{s2}{the letter c}{ca\pgfparserswitch{initial}}
\pgfparserdef{myparser2}{initial}{the letter b}{c}
\pgfparserdef{myparser2}{initial}{the letter c}{b}
\pgfparserdef{myparser2}{initial}{the character ;}{\pgfparserswitch{final}}

\newcommand\myparserone[1]{%
  \expandafter\pgfparserparse\expandafter{\expandafter myparser\expandafter}#1;%
}

\newcommand\myparsertwo[1]{%
  \expandafter\pgfparserparse\expandafter{%
    \expandafter myparser2\expandafter}#1;%
}

\begin{document}
\textbf{\pgfparserparse{myparser}caac; \pgfparserparse{myparser2}abbcac;}
\emph{\myparserone{caac} \myparsertwo{abbcac}}
\end{document}

The result:

parsers results

Thanks, this is a really nice solution. This would be even better if we can produce the parser automatically from the code... — Xoff, Jul 20 '12 at 06:21
@Xoff: citation: "The syntax for the code definition is not important." ;-) — Paul Gaborit, Jul 20 '12 at 06:25
You're right, and it is enough for what I need. Thank you :) — Xoff, Jul 20 '12 at 06:28

Macro for a code translator

2 Answers2

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