@c -*-texinfo-*-
@c This is part of the GNU Guile Reference Manual.
@c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2005, 2010, 2011
@c   Free Software Foundation, Inc.
@c See the file guile.texi for copying conditions.

@node Parallel Installations
@section Parallel Installations

@cindex pkg-config
@cindex effective version

Guile provides strong API and ABI stability guarantees during stable
series, so that if a user writes a program against Guile version 2.0.3,
it will be compatible with some future version 2.0.7.  We say in this
case that 2.0 is the @dfn{effective version}, composed of the major and
minor versions, in this case 2 and 0.

Users may install multiple effective versions of Guile, with each
version's headers, libraries, and Scheme files under their own
directories.  This provides the necessary stability guarantee for users,
while also allowing Guile developers to evolve the language and its
implementation.

However, parallel installability does have a down-side, in that users
need to know which version of Guile to ask for, when they build against
Guile.  Guile solves this problem by installing a file to be read by the
@code{pkg-config} utility, a tool to query installed packages by name.
Guile encodes the version into its pkg-config name, so that users can
ask for @code{guile-2.0} or @code{guile-2.2}, as appropriate.

For effective version @value{EFFECTIVE-VERSION}, for example, you would
invoke @code{pkg-config --cflags --libs guile-@value{EFFECTIVE-VERSION}}
to get the compilation and linking flags necessary to link to version
@value{EFFECTIVE-VERSION} of Guile.  You would typically run
@code{pkg-config} during the configuration phase of your program and use
the obtained information in the Makefile.

See the @code{pkg-config} man page, for more information, or its web
site, @url{http://pkg-config.freedesktop.org/}.

@xref{Autoconf Support}, for more on checking for Guile from within a
@code{configure.ac} file.


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