Non-letters in macro names

New LaTeX users are often surprised that macro definitions containing non-letters, such as

\newcommand{\cul8r}{Goodbye!}

fail to compile. The reason is that the TeX macro language, unlike most programming languages, allows nothing but letters in macro names.

There are a number of techniques for defining a macro with a name like \cul8r. Unfortunately, none of the techniques is particularly good:

Use \csname…\endcsname to define and invoke the macro:
```
\expandafter\newcommand\csname cul8r\endcsname{Goodbye!}
I said, ``\csname cul8r\endcsname''.
```
- Pro: No unexpected side effects
- Con: So verbose as to be unusable
Define a “special-command generator”, and use the resulting commands:
```
\newcommand{\DefineRemark}[2]{%
  \expandafter\newcommand\csname rmk-#1\endcsname{#2}%
}
\newcommand{\Remark}[1]{\csname rmk-#1\endcsname}
...
\DefineRemark{cul8r}{Goodbye!}
...
\Remark{cul8r}
```
- Pro: Straightforward to use, not too untidy
- Con: It’s hardly doing what we set out to do (experts will see that you are defining a macro, but others likely won’t)
Convince TeX that 8 is a letter:
```
\catcode`8 = 11 
\newcommand{\cul8r}{Goodbye!}
I said, ``\cul8r''.
```
- Pro: \cul8r can be used directly
- Con: Likely to break other uses of 8 (such as numbers or dimensions; so \setlength{\paperwidth}{8in} tells us: ```latex ! Missing number, treated as zero.
8 ``` As a general rule, changing category codes is something to use _in extremis_, after detailed examination of options. It is conceivable that such drastic action could be useful for you, but most ordinary users are well advised not even to try such a technique.
Define a macro \cul which must always be followed by 8r:
```
\def\cul8r{Goodbye!}
I said, ``\cul8r''.
```
- Pro: \cul8r can be used directly
- Con #1: Breaks if \cul is followed by anything other than 8r, with a confusing diagnostic — \cul99 produces:
```
! Use of \cul doesn't match its definition.
<*> \cul9
       9
```
  (which would confuse someone who hadn’t even realised there was a definition of \cul in the document).
- Con #2: Silently redefines existing \cul, if any; as a result, the technique cannot be used to define both a \cul8r and, say, a \cul123 macro in the same document.

Technique 3 is in fact commonly used — in a limited form — within most LaTeX packages and within LaTeX itself. The convention is to use @ within the names of internal macros to hide them from the user and thereby prevent naming conflicts. To this end, LaTeX automatically treats @ as a letter while processing classes and packages and as a non-letter while processing the user’s document. The key to this technique is the separation: internally a non-letter is used for macro names, and the user doesn’t see anything of it, while the status remains “frozen” in all the definitions created within the class or package. See \@ and @ in macro names for more information.

Note that analogous use of technique 3 in this example would give us

\begingroup
  \catcode`8 = 11 
  \gdef\cul8r{Goodbye!}
  \gdef\later{\cul8r}
\endgroup
I said, ``\later''.

which works, but rather defeats the object of the exercise. (\later has the “frozen” catcode for “8”, even though the value has reverted to normal by the time it’s used; note, also, the use of the primitive command \gdef, since \newcommand can’t make a macro that’s available outside the group.)

Recommendation: Either choose another mechanism (such as \DefineRemark above), or choose another name for your macro, one that contains only ordinary letters. A common approach is to use roman numerals in place of arabic ones:

\newcommand{\culVIIIr}{Goodbye!}

which rather spoils the intent of the joke implicit in the example \cul8r!

FAQ ID: Q-linmacnames
Tags: macros