dnl AS_AC_EXPAND(VAR, CONFIGURE_VAR)

 dnl

 dnl example

 dnl AS_AC_EXPAND(SYSCONFDIR, $sysconfdir)

 dnl will set SYSCONFDIR to /usr/local/etc if prefix=/usr/local

 AC_DEFUN([AS_AC_EXPAND],

 [

   EXP_VAR=[$1]

   FROM_VAR=[$2]

   dnl first expand prefix and exec_prefix if necessary

   prefix_save=$prefix

   exec_prefix_save=$exec_prefix

   dnl if no prefix given, then use /usr/local, the default prefix

   if test "x$prefix" = "xNONE"; then

     prefix=$ac_default_prefix

   fi

   dnl if no exec_prefix given, then use prefix

   if test "x$exec_prefix" = "xNONE"; then

     exec_prefix=$prefix

   fi

   full_var="$FROM_VAR"

   dnl loop until it doesn't change anymore

   while true; do

     new_full_var="`eval echo $full_var`"

     if test "x$new_full_var"="x$full_var"; then break; fi

     full_var=$new_full_var

   done

   dnl clean up

   full_var=$new_full_var

   AC_SUBST([$1], "$full_var")

   dnl restore prefix and exec_prefix

   prefix=$prefix_save

   exec_prefix=$exec_prefix_save

 ])