19.3 Macro Details and Caveats

By design, macro expansion does not happen in the following contexts in makeinfo:

• @macro and @unmacro lines;
• @if... lines, including @ifset and similar;
• @set, @clear, @value;
• @clickstyle lines;
• @end lines.

Unfortunately, TeX may do some expansion in these situations, possibly yielding errors.

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 makeinfo by invoking texi2dvi with the ‘-E’ option (see section Format with texi2dvi). Or, more reliably, eschew Texinfo macros altogether and use a language designed for macro processing, such as M4 (see section External Macro Processors: Line Directives).

• As mentioned earlier, macro names must consist entirely of letters.
• 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.
• All macros are expanded inside at least one TeX group.
• Macro arguments cannot cross lines.
• 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 @example environments, may behave unpredictably in TeX.
• White space is ignored at the beginnings of lines.
• Macros can’t be reliably used in the argument to accent commands (see section Inserting Accents).
• The backslash escape for commas in macro arguments does not work; @comma{} must be used.
• As a consequence, if a macro takes two or more arguments, and you want to pass an argument with the Texinfo command @, (to produce a cedilla, see section Inserting Accents), you have to use @value or another work-around. Otherwise, TeX takes the comma as separating the arguments. Example:

  @macro mactwo{argfirst, argsecond}
  \argfirst\+\argsecond\.
  @end macro
  @set fc Fran@,cois
  @mactwo{@value{fc}}
  

  produces:

  François+.
  

  The natural-seeming @mactwo{Fran@,cois} passes the two arguments ‘Fran@’ and ‘cois’ to the macro, and nothing good results. And, as just mentioned, although the comma can be escaped with a backslash for makeinfo (‘@\,’), that doesn’t work in TeX, so there is no other solution.

• It is usually best to avoid comments inside macro definitions, but see the next item.
• In general, the interaction of newlines in the macro definitions and invocations depends on the precise commands and context, notwithstanding the previous statements. You may be able to work around some problems with judicious use of @c. Suppose you define a macro that is always used on a line by itself:

  @macro linemac
  @cindex whatever @c
  @end macro
  ...
  foo
  @linemac
  bar
  

  Without the @c, there will be a unwanted blank line between the ‘@cindex whatever’ and the ‘bar’ (one newline comes from the macro definition, one from after the invocation), causing an unwanted paragraph break.

  On the other hand, you wouldn’t want the @c if the macro was sometimes invoked in the middle of a line (the text after the invocation would be treated as a comment).

• In general, you can’t arbitrarily substitute a macro (or @value) 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:

  @macro offmacro
  off
  @end macro
  @headings @offmacro
  

  This looks equivalent to @headings off, but for TeXnical reasons, it fails with a mysterious error message (namely, ‘Paragraph ended before @headings was complete’).

• Macros cannot define macros in the natural way. To do this, you must use conditionals and raw TeX. For 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
  

The makeinfo implementation also has the following limitations (by design):

• @verbatim and macros do not mix; for instance, you can’t start a verbatim block inside a macro and end it outside (see section @verbatim: Literal Text). Starting any environment inside a macro and ending it outside may or may not work, for that matter.
• Macros that completely define macros are ok, but it’s not possible to have incompletely nested macro definitions. That is, @macro and @end macro (likewise for @rmacro) must be correctly paired. For example, you cannot start a macro definition within a macro, and then end that nested definition outside the macro.

In the makeinfo implementation before Texinfo 5.0, ends of lines from expansion of an @macro definition did not end an @-command line-delimited argument (@chapter, @center, etc.). This is no longer the case. For example:

@macro twolines{}
aaa
bbb
@end macro
@center @twolines{}

In the current makeinfo, this is equivalent to:

@center aaa
bbb

with just ‘aaa’ as the argument to @center. In the earlier implementation, it would have been parsed as this:

@center aaa bbb

This document was generated on October 2, 2013 using texi2html 5.0.