### 19.1 Defining Macros

You use the Texinfo `@macro` command to define a macro, like this:

```@macro macroname{param1, param2, …}
text … \param1\ …
@end macro
```

The parameters param1, param2, … correspond to arguments supplied when the macro is subsequently used in the document (described in the next section).

For a macro to work consistently with TeX, macroname must consist entirely of letters: no digits, hyphens, underscores, or other special characters. So, we recommend using only letters. However, `makeinfo` will accept anything consisting of alphanumerics, and (except as the first character) ‘-’. The ‘_’ character is excluded so that macros can be called inside `@math` without a following space (see Inserting Math).

If a macro needs no parameters, you can define it either with an empty list (‘@macro foo {}’) or with no braces at all (‘@macro foo’).

The definition or body of the macro can contain most Texinfo commands, including macro invocations. However, a macro definition that defines another macro does not work in TeX due to limitations in the design of `@macro`.

In the macro body, instances of a parameter name surrounded by backslashes, as in ‘\param1\’ in the example above, are replaced by the corresponding argument from the macro invocation. You can use parameter names any number of times in the body, including zero.

To get a single ‘\’ in the macro expansion, use ‘\\’. Any other use of ‘\’ in the body yields a warning.

The newline characters after the `@macro` line and before the `@end macro` line are ignored, that is, not included in the macro body. All other whitespace is treated according to the usual Texinfo rules. However, there are still undesirable and unpredictable interactions between newlines, macros, and commands which are line-delimited, as warned about below (see Macro Details).

To allow a macro to be used recursively, that is, in an argument to a call to itself, you must define it with ‘@rmacro’, like this:

```@rmacro rmac {arg}
a\arg\b
@end rmacro
…
@rmac{1@rmac{text}2}
```

This produces the output ‘a1atextb2b’. With ‘@macro’ instead of ‘@rmacro’, an error message is given.

You can undefine a macro foo with `@unmacro foo`. It is not an error to undefine a macro that is already undefined. For example:

```@unmacro foo
```