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I try do define a macro \onoff, which alternatively prints "on" and "off" each time it's used. For example the sequence \onoff \onoff \onoff would print on off on
My first guess would be to use the following code:
\def\a{on}
\def\b{off}
\newcommand\onoff{\a\def\c{\a}\def\a{\b}\def\b{\c}}
However this code doesn't work. Is there an elegant way to code this?
One way
\documentclass{article}
\makeatletter
\def\@ONoff {on\let\onoff\@onOFF}
\def\@onOFF {off\let\onoff\@ONoff}
\let\onoff\@ONoff
\makeatother
\begin{document}
\onoff\onoff\onoff\onoff\onoff\onoff...
\end{document}
Another way (was a now deleted separate answer)
\documentclass{article}
\makeatletter
\def\onoff{\@onoff{on}{off}}
\def\@onoff #1#2{#1\def\onoff {\@onoff{#2}{#1}}}
\makeatother
\begin{document}\thispagestyle{empty}
\onoff\onoff\onoff\onoff\onoff\onoff...
\end{document}
A third way
\documentclass{article}
\makeatletter
\def\onoff {\onoroff{on\let\onoroff\@secondoftwo}{off\let\onoroff\@firstoftwo}}
\let\onoroff\@firstoftwo
\makeatother
\begin{document}
\onoff\onoff\onoff\onoff\onoff\onoff\onoff...
\onoff\onoff\onoff\onoff\onoff...
\end{document}
Using etoolbox and bools and the greatest TikZ-foo i have ever produced.
\documentclass{article}
\usepackage{etoolbox}
\usepackage{parskip}
\usepackage{tikz}
\newbool{volt}
\newcommand{\onoff}{%
\ifbool{volt}{%
\boolfalse{volt}\candleOn\space ON}{%
\booltrue{volt}\candleOff\space OFF}%
}
\newcommand{\candleOff}{\tikz \draw (0,0) rectangle
(.2,.8);}
\newcommand{\candleOn}{\begin{tikzpicture}\draw (0,0) rectangle
(.2,.8);\draw [fill=orange] (.1,.9) circle
[radius=.1];\end{tikzpicture}}
\begin{document}
\onoff\par
\onoff\par
\onoff\par
\onoff\par
\end{document}
etoolbox's bools have (in functionality or readability) over the similar use of conditionals described by @egreg below (tex.stackexchange.com/a/232062/1169)? (Of course, egreg's answer doesn't include the stunning TikZ-foo. :-) )
etoolbox gives a bunch of higher-level commands, no need for @-catcode hackery in most cases. Features like the ones described in the answers here are mostly needed by class/package authors, users just the functionality of the end result (on/off).
Mar 9 '15 at 8:10
Use a conditional
\documentclass{article}
\newif\ifoff
\newcommand{\onoff}{%
\relax\ifoff off\global\offfalse\else on\global\offtrue\fi
}
\begin{document}
\onoff
\onoff
\onoff
\end{document}
or a counter
\documentclass{article}
\newcount\offcount
\newcommand{\onoff}{%
\relax
\ifodd\offcount
\global\advance\offcount 1
off%
\else
\global\advance\offcount -1
on%
\fi
}
\begin{document}
\onoff
\onoff
\onoff
\end{document}
In both cases, if you want only local redefinitions, remove \global.
Note the starting \relax, necessary if you want to use \onoff in tables.
An abstract version, with the help of etoolbox that makes things a bit easier with toggles (it could be realized with conditionals).
\documentclass{article}
\usepackage{etoolbox}
\newcommand{\newalternatingcommand}[3]{%
\newcommand{#1}{%
\iftoggle{\string#1}
{#2\global\togglefalse{\string#1}}
{#3\global\toggletrue{\string#1}}%
}%
\newtoggle{\string#1}%
\toggletrue{\string#1}%
}
\newalternatingcommand{\onoff}{on}{off}
\begin{document}
\onoff
\onoff
\onoff
\end{document}
\iftoggle uses just one control sequence, while \ifbool uses three. But the advantage is mostly in the fact we can use \string#1 in the argument of \iftoggle and a simpler syntax for the two cases.
For example:
\def\onoffA{on\gdef\onoff{off\global\let\onoff=\onoffA}} \let\onoff=\onoffA
Test: \onoff, \onoff, \onoff, \onoff, \onoff, \onoff.
\bye
\def\onoff{\a\let\c\a\let\a\b\let\b\c}in your set-up works.\edefwould do as well.\def\c{\a}says "define\cto expand to\a" (thus eventually to the future contents of\a), not "… to the (current) contents of\a".\letessentially says the latter.\edefexpands macros at definition time rather than use time, which is why it would also work here.