Correct way to define macros \etc \ie in latex

Question

In this article the author discusses the use of \@ to put correct spacings after full stops that are not at the end of a sentence e.g. Mr. i.e. etc.

The macro suggested

\newcommand\etc{etc\@ifnextchar.{}{.\@}}

is not quite perfect since in the case (\etc more text) it produces (etc.more text).

I have seen a lot of authors who have made their own versions of the \etc macro, mostly variations on etc.\.

What macros for \etc, \ie, \etal, \eg produce the nicest results in the most situations?

Is this something too personal in taste to be solved in general?

Answer 1

All LaTeX commands eliminate space after them. If you want a space, you need to escape it:

\etc\ and more

This is necessary, because you need to be clear where the command name ends. \etcno space cannot be correctly interpreted.

Answer 2

Earlier I used macros for "et al.", etc., but nowadays I would discourage people from defining that kind of macros.

One problem is what you already observed: it's surprisingly tricky to get the definitions right so that they handle all special cases correctly (including the interactions with other packages – e.g., those that re-define the "\cite" command and tweak spacing before references).

But more importantly, even if you have a bunch of macros that suit your needs and you know how to use them, your co-authors are likely to be confused with exactly how to use your macros correctly in various special cases.

Hence I'd recommend that you avoid macros for trivial things such as "et al." and simply spell out everything by using standard Latex markup. After all, most cases don't need any special handling ("e.g." is often followed by a comma; "et al." is often followed by "~\cite", etc.), and whenever special handling is needed, all Latex users should know how to use commands such as "\ " and "\@".

Answer 3

A technical challenge! We can avoid the problem of letters after spaces by looking at the catcode of the next character and seeing whether or not it is a letter; this can be done with the Latex3's expl3 macro \peek_charcode:NTF (my first expl3 code!):

\documentclass{article}

\usepackage{expl3}
\ExplSyntaxOn
\newcommand\latinabbrev[1]{
  \peek_meaning:NTF . {% Same as \@ifnextchar
    #1\@}%
  { \peek_catcode:NTF a {% Check whether next char has same catcode as \'a, i.e., is a letter
      #1.\@ }%
    {#1.\@}}}
\ExplSyntaxOff

%Omit final dot from each def.
\def\eg{\latinabbrev{e.g}}
\def\etal{\latinabbrev{et al}}
\def\etc{\latinabbrev{etc}}
\def\ie{\latinabbrev{i.e}}

\begin{document}

Maybe a list, \eg, a, b, c, and d.  Which is to say (\ie) a, b, \etc.  Consider Knuth, \cf The TeXbook.

\end{document}

Jukka's advice I think is sound, though: I'd say the problem Will works around with his \etc macro we should see as a bug in Tex's implementation of double spacing (Will Robertson should ask for his cheque): if you know the bug is there, you can workaround it directly by putting in \@ in cases such as ".)", or you can have tricky code that means you don't have to think in this case, but you have added complexity to the way you typeset which is not going to work for you with the next unexpected glitch, one you probably have introduced yourself.

Postscript Previous version fixed, thanks to Joseph Wright noticing a stupid error at tex.stackexchange.com.

Answer 4

Have you tried using the xspace package?

Example macro:

\def\etc{etc.\@\xspace}

Some tests:

Cat, dog, \etc. And so on.   \\
Cat, dog, \etc! And so on.   \\
Cat, dog, \etc, and so on.   \\
Cat (dog, \etc). And so on.  \\

Produces:

---

From the documentation:

The xspace package provides a single command that looks at what comes after it in the command stream, and decides whether to insert a space to replace one "eaten" by the TeX command decoder.