How do you swap the commands for two symbols?

Question

I find that I much prefer \varphi to \phi and generally would rather use the \varphi than the \phi. But it's three more characters to type \varphi instead of \phi, which is most troublesome. So I would like to swap the two commands. I tried a couple of things on my own, but one resulted in an infinite loop in compilation and the other led to \varphi taking over all of the \phi commands I made. What would be the correct way to do this?

@Gonzalo This defines '\phi' to be '\varphi', but doesn't define '\varphi' to be the "old" '\phi'. — JSchlather, Apr 01 '12 at 18:38
The idea is the same: \let\oldphi\phi \let\phi\varphi \let\varphi\oldphi — Gonzalo Medina, Apr 01 '12 at 18:42
I usually say to go with \let\phi\varphi, as the two symbols very rarely are used together in the same document (a polite way to say: "never use both in the same document"). — egreg, Apr 01 '12 at 20:49
@egreg: Never say never. An obvious example of using both in the same document is a document explaining the difference between \phi and \varphi. — celtschk, Apr 02 '12 at 09:01

score 40 · Accepted Answer · answered Apr 01 '12 at 18:41

40

Try the following:

$\phi\varphi$
\let\temp\phi
\let\phi\varphi
\let\varphi\temp
$\phi\varphi$

answered Apr 01 '12 at 18:41

André

2,345

2

Okay, so my issue before is that I was using \renewcommand instead of \let. Could you elaborate on the differences between the two commands? – JSchlather Apr 01 '12 at 18:49
9

\let\a\b makes \a have the definition that \b has so \let\a\a is a no-op \newcommand\a{\b} makes a expand to \b so \newcommand\a{\a} makes a expand to itself and loop forever – David Carlisle Apr 01 '12 at 18:57
5

@DavidCarlisle Okay so it's essentially hard linking versus symbolic linking. Which is what I suspected the issue was. Thanks. – JSchlather Apr 01 '12 at 19:04

score 40 · Answer 2 · answered Apr 01 '12 at 18:55

40

The usual way to exchange two values is to use a temporary command name to store one of them while swapping, but if, for no particular reason, you want to avoid the extra command name then:

\documentclass{article}

\begin{document}

$\phi\varphi$


\expandafter\mathchardef\expandafter\varphi\number\expandafter\phi\expandafter\relax
\expandafter\mathchardef\expandafter\phi\number\varphi

$\phi\varphi$


\end{document}

answered Apr 01 '12 at 18:55

David Carlisle

757,742

haha, saving up just that extra bit of namespace! – romeovs Apr 01 '12 at 19:04
15

What the…?! Cool! :-D – morbusg Apr 01 '12 at 19:09
I see, you are using the input stream as temporary storage. – Ryan Reich Jun 26 '12 at 23:55

score 17 · Answer 3 · answered Apr 01 '12 at 18:46

17

For non-complex macros, using an interim macro to swap definitions is sufficient. However, if the macros (say, funcA and funcB) takes optional arguments, you need to use a different approach via letltxmacro's macro \LetLtxMacro{<new macro>}{<old macro>}:

\usepackage{letltxmacro}% http://ctan.org/pkg/letltxmacro
%...
\LetLtxMacro{\temp}{\funcA}
\LetLtxMacro{\funcA}{\funcB}
\LetLtxMacro{\funcB}{\temp}

answered Apr 01 '12 at 18:46

Werner

603,163

2

+1 for giving an answer with less \expandafters but more use than mine. – David Carlisle Apr 01 '12 at 20:36

How do you swap the commands for two symbols?

3 Answers3

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