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<a name="Macro-Details"></a>
<div class="header">
<p>
Next: <a href="_0040alias.html#g_t_0040alias" accesskey="n" rel="next"><code>@alias</code></a>, Previous: <a href="Invoking-Macros.html#Invoking-Macros" accesskey="p" rel="prev">Invoking Macros</a>, Up: <a href="Defining-New-Texinfo-Commands.html#Defining-New-Texinfo-Commands" accesskey="u" rel="up">Defining New Texinfo Commands</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html#Command-and-Variable-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Macro-Details-and-Caveats"></a>
<h3 class="section">17.3 Macro Details and Caveats</h3>
<a name="index-Macro-details"></a>
<a name="index-Details-of-macro-usage"></a>
<a name="index-Caveats-for-macro-usage"></a>

<a name="index-Macro-expansion_002c-contexts-for"></a>
<a name="index-Expansion-of-macros_002c-contexts-for"></a>
<p>By design, macro expansion does not happen in the following contexts
in <code>makeinfo</code>:
</p>
<ul>
<li> <code>@macro</code> and <code>@unmacro</code> lines;

</li><li> <code>@if...</code> lines, including <code>@ifset</code> and similar;

</li><li> <code>@set</code>, <code>@clear</code>, <code>@value</code>;

</li><li> <code>@clickstyle</code> lines;

</li><li> <code>@end</code> lines.
</li></ul>

<p>Unfortunately, TeX may do some expansion in these situations,
possibly yielding errors.
</p>
<p>Also, quite a few macro-related constructs cause problems with TeX;
some of the caveats are listed below.  Thus, if you get macro-related
errors when producing the printed version of a manual, you might try
expanding the macros with <code>makeinfo</code> by invoking
<code>texi2dvi</code> with the &lsquo;<samp>-E</samp>&rsquo; option (see <a href="Format-with-texi2dvi.html#Format-with-texi2dvi">Format with <code>texi2dvi</code></a>).  Or, more reliably, eschew Texinfo macros altogether
and use a language designed for macro processing, such as M4
(see <a href="External-Macro-Processors.html#External-Macro-Processors">External Macro Processors</a>).
</p>
<ul>
<li> As mentioned earlier, macro names must consist entirely of letters.

</li><li> It is not advisable to redefine any TeX primitive, plain, or
Texinfo command name as a macro. Unfortunately this is a large and
open-ended set of names, and the possible resulting errors are
unpredictable.

</li><li> Arguments to macros taking more than one argument cannot cross lines.

</li><li> Macros containing a command which must be on a line by itself, such as
a conditional, cannot be invoked in the middle of a line.  Similarly,
macros containing line-oriented commands or text, such as
<code>@example</code> environments, may behave unpredictably in TeX.

</li><li> Texinfo commands in the expansion of a macro in the text of an index 
entry may end up being typeset as literal text (including an &ldquo;@&rdquo; 
sign), instead of being interpreted with their intended meaning.

</li><li> White space is ignored at the beginnings of lines.

</li><li> Macros can&rsquo;t be reliably used in the argument to accent commands
(see <a href="Inserting-Accents.html#Inserting-Accents">Inserting Accents</a>).

</li><li> The backslash escape for commas in macro arguments does not work;
<code>@comma{}</code> must be used.

</li><li> Likewise, if you want to pass an argument with the Texinfo command 
<code>@,</code> (to produce a cedilla, see <a href="Inserting-Accents.html#Inserting-Accents">Inserting Accents</a>), you have 
to use <code>@value</code> or another work-around.  Otherwise, the comma
may be taken as separating the arguments.  For example,

<div class="example">
<pre class="example">@macro mactwo{argfirst, argsecond}
\argfirst\+\argsecond\.
@end macro
@set fc Fran@,cois
@mactwo{@value{fc},}
</pre></div>

<p>produces:
</p>
<div class="display">
<pre class="display">Fran&ccedil;ois+.
</pre></div>


</li><li> Ending a macro body with &lsquo;<samp>@c</samp>&rsquo; may cause text following the macro
invocation to be ignored as a comment in <code>makeinfo</code>.  This is 
not the case when processing with TeX (in case you really want to 
comment out following text, use &lsquo;<samp>@comment</samp>&rsquo; instead).  This was
often done to &ldquo;comment out&rdquo; an unwanted newline at the end of a macro 
body, but this is not necessary any more, as the final newline before 
&lsquo;<samp>@end macro</samp>&rsquo; is not included in the macro body anyway.

</li><li> In general, you can&rsquo;t arbitrarily substitute a macro (or
<code>@value</code>) call for Texinfo command arguments, even when the text
is the same.  Texinfo is not M4 (or even plain TeX).  It might work
with some commands, it fails with others.  Best not to do it at all.
For instance, this fails:

<div class="example">
<pre class="example">@macro offmacro
off
@end macro
@headings @offmacro
</pre></div>

<p>This looks equivalent to <code>@headings off</code>, but for TeXnical
reasons, it fails with a mysterious error message (namely,
&lsquo;<samp>Paragraph ended before @headings was complete</samp>&rsquo;).
</p>
</li><li> Macros cannot define macros in the natural way.  To do this, you must
use conditionals and raw TeX.  For example:

<div class="example">
<pre class="example">@ifnottex
@macro ctor {name, arg}
@macro \name\
something involving \arg\ somehow
@end macro
@end macro
@end ifnottex
@tex
\gdef\ctor#1{\ctorx#1,}
\gdef\ctorx#1,#2,{\def#1{something involving #2 somehow}}
@end tex
</pre></div>
</li></ul>

<p>The <code>makeinfo</code> implementation also has the following
limitations (by design):
</p>
<ul>
<li> <code>@verbatim</code> and macros do not mix; for instance, you can&rsquo;t start
a verbatim block inside a macro and end it outside
(see <a href="_0040verbatim.html#g_t_0040verbatim"><code>@verbatim</code></a>).  Starting any environment inside a macro
and ending it outside may or may not work, for that matter.

</li><li> Macros that completely define macros are ok, but it&rsquo;s not possible to
have incompletely nested macro definitions.  That is, <code>@macro</code>
and <code>@end macro</code> (likewise for <code>@rmacro</code>) must be
correctly paired.  For example, you cannot start a macro definition
within a macro, and then end that nested definition outside the macro.
</li></ul>

<p>In the <code>makeinfo</code> implementation before Texinfo 5.0, ends of
lines from expansion of a <code>@macro</code> definition did not end an
@-command line-delimited argument (<code>@chapter</code>, <code>@center</code>,
etc.).  This is no longer the case.  For example:
</p>
<div class="example">
<pre class="example">@macro twolines{}
aaa
bbb
@end macro
@center @twolines{}
</pre></div>

<p>In the current <code>makeinfo</code>, this is equivalent to:
</p>
<div class="example">
<pre class="example">@center aaa
bbb
</pre></div>

<p>with just &lsquo;<samp>aaa</samp>&rsquo; as the argument to <code>@center</code>.  In
the earlier implementation, it would have been parsed as this:
</p>
<div class="example">
<pre class="example">@center aaa bbb
</pre></div>


<hr>
<div class="header">
<p>
Next: <a href="_0040alias.html#g_t_0040alias" accesskey="n" rel="next"><code>@alias</code></a>, Previous: <a href="Invoking-Macros.html#Invoking-Macros" accesskey="p" rel="prev">Invoking Macros</a>, Up: <a href="Defining-New-Texinfo-Commands.html#Defining-New-Texinfo-Commands" accesskey="u" rel="up">Defining New Texinfo Commands</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html#Command-and-Variable-Index" title="Index" rel="index">Index</a>]</p>
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