undefining custom commands [duplicate]

Question

Possible Duplicate:
How to undo a \def (i.e., Need a \undef capability)

After you define a command using \newcommand, is it possible to undefine it?

My motivation is that I'm writing a thesis, where each chapter is in a separate source file. Some chapters define their own commands that are used nowhere else, so I'd like them to be visible only within that chapter.

I'd therefore like to be able to do something like:

\chapter{Some Chapter}
\newcommand{foo}{...}
... % chapter body
\forgetcommand{foo}
% end of chapter

Is there anything like the fictitious \forgetcommand macro above?

Answer 1

If your concern is whether or not a command exists and you want to define/redefine it, LaTeX provides \providecommand which has a similar interface as \newcommand and \renewcommand. It does the appropriate (re)definition where necessary.

Alternatively, if you want to "undefine" a command \foo, you could also just use \let\foo\undefined.

Answer 2

If the macro is used nowhere else, there's no problem leaving it defined surely.

Rather than encapsulation, you could consider name-spacing your chapter specific macros.

So macros used only in chapter one look like this: \chaponefoo… while macros from chapter three will be: \chapthreefoo… and so on.

(My previous answer had some problems, and Werner's answer is better.)

Answer 3

Consider the following example. It shows the way as Seamus suggested and the way with \let...\undefined.

\documentclass{minimal}

\newcommand{\foo}{Foo}
\newcommand{\baz}{Baz}

\begin{document}
x\foo\baz x

\renewcommand{\foo}{}
\let\baz\undefined

x\foo%
%\baz x% can’t use \baz anymore

%\newcommand{\foo}{FOO}% doesn?t work
\renewcommand{\foo}{FOO}% still need \renew...
\newcommand{\baz}{BAZ}

x\foo\baz x
\end{document}

\foo dosen’t produce an output anymore but can’t be defined a second time (it still needs the \renew… command). \baz is removed an can be defined a second time.