A macro that you write might need to use values that have previously
been computed by other macros. For example,
examines the output of
lex, so it depends on
AC_PROG_LEX having been called first to set the shell variable
Rather than forcing the user of the macros to keep track of the
dependencies between them, you can use the
AC_REQUIRE macro to do
AC_REQUIRE can ensure that a macro is only
called if it is needed, and only called once.
m4macro macro-name has not already been called, call it (without any arguments). Make sure to quote macro-name with square brackets. macro-name must have been defined using
AC_DEFUNor else contain a call to
AC_PROVIDEto indicate that it has been called.
An alternative to using
AC_DEFUN is to use
define and call
AC_PROVIDE. Because this technique does not prevent nested
messages, it is considered obsolete.
AC_PROVIDE. An easy way to get it is from the
$0, like this:
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