+dnl Check for Guile-zlib.
+GUILE_MODULE_AVAILABLE([have_guile_zlib], [(zlib)])
+if test "x$have_guile_zlib" != "xyes"; then
+ AC_MSG_ERROR([Guile-zlib is missing; please install it.])
+fi
+
+dnl Check for Guile-lzlib.
+GUILE_MODULE_AVAILABLE([have_guile_lzlib], [(lzlib)])
+if test "x$have_guile_lzlib" != "xyes"; then
+ AC_MSG_ERROR([Guile-lzlib is missing; please install it.])
+fi
+
+dnl Check for Guile-Avahi.
+GUILE_MODULE_AVAILABLE([have_guile_avahi], [(avahi)])
+AM_CONDITIONAL([HAVE_GUILE_AVAHI],
+ [test "x$have_guile_avahi" = "xyes"])
+