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guile.m4 may need serial number

From: Mike Gran
Subject: guile.m4 may need serial number
Date: Thu, 27 Dec 2007 08:39:52 -0800 (PST)

The automake manual recommends that .m4 files use a serial number for 
versioning, so that it is possible to tell when an .m4 installed by aclocal is 

Because third-party macros defined in ‘*.m4’ files are naturally shared between 
projects, some people like to version them. This makes it easier to tell which 
of two M4
files is newer. Since at least 1996, the tradition is to use a ‘#serial’ line 
for this.
A serial number should be a single line of the form
# serial version
where version is a version number containing only digits and dots. Usually 
people use a
single integer, and they increment it each time they change the macro (hence 
the name of
“serial”). Such a line should appear in the M4 file before any macro definition.
The ‘#’ must be the first character on the line, and it is OK to have extra 
words after
the version, as in
#serial version garbage
Normally these serial numbers are completely ignored by aclocal and autoconf, 
any genuine comment. However when using aclocal’s ‘--install’ feature, these 
numbers will modify the way aclocal selects the macros to install in the 
package: if two
files with the same basename exists in your search path, and if at least one of 
them use a
‘#serial’ line, aclocal will ignore the file that has the older ‘#serial’ line 
(or the file that
has none).


Mike Gran

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