ac_cond_with

actually used after an AC_ARG_WITH(PKG,...) option-directive, where AC_ARG_WITH is a part of the standard autoconf to define a `configure` --with-PKG option.

the AC_COND_WITH(PKG) will use the $with_PKG var to define WITH_PKG and WITHOUT_PKG substitutions (AC_SUBST), that are either '' or '#' - depending whether the var was "no" or not (probably 'yes', or a value); it will also declare WITHVAL_PKG for use when someone wanted to set a val other than just "yes". And there is a WITHDEF_PKG that expands to a C-precompiler definition of the form -DWITH_PKG or -DWITH_PKG=\"value\" (n.b.: the PKG *is* uppercased if in lowercase and "-" translit to "_")

this macro is most handily in making Makefile.in/Makefile.am that have a set of if-with declarations that can be defined as follows: CFLAGS = -Wall @WITHOUT_FLOAT@ -msoft-float # --without-float @WITH_FLOAT@ LIBS += -lm # --with-float DEFS += -DNDEBUG @WITHDEF_MY_PKG@ # --with-my-pkg="/usr/lib" DEFS += @WITHVAL_DEFS@ # --with-defs="-DLOGLEVEL=6"

example configure.in: AC_ARG_WITH(float, [ --with-float, with float words support]) AC_COND_WITH(float,no)

extened notes: 1. the idea comes from AM_CONDITIONAL but it is much easier to use,
    and unlike automake's ifcond, the Makefile.am will work as a
    normal $(MAKE) -f Makefile.am makefile.
2. the @VALS@ are parsed over by automake so automake will see all
    the filenames and definitions that follow @WITH_FLOAT@, so that
    the AC_COND_WITH user can see additional message if they apply.
3. in this m4-part, there's a AC_ARG_COND_WITH with the synopsis of
      AC_ARG_WITH and an implicit following AC_COND_WITH   =:-)
4. and there is an AC_ARG_COND_WITH_DEFINE that will emit an
      implicit AC_DEFINE that is actually seen by autoheader, even
      generated with the correct name and comment, for config.h.in

some non-autoconf coders tend to create "editable" Makefile where they have out-commented lines with an example (additional) definition. Each of these can be replaced with a three-liner in configure.in as shown above. Starting to use AC_COND_WITH will soon lead you to provide a dozen --with-option rules for the `configure` user. Do it!

AC_DEFUN([AC_COND_WITH],
[dnl the names to be defined...
pushdef([WITH_VAR],    patsubst([with_$1], -, _))dnl
pushdef([VAR_WITH],    patsubst(translit([with_$1], [a-z], [A-Z]), -, _))dnl
pushdef([VAR_WITHOUT], patsubst(translit([without_$1], [a-z], [A-Z]), -, _))dnl
pushdef([VAR_WITHVAL], patsubst(translit([withval_$1], [a-z], [A-Z]), -, _))dnl
pushdef([VAR_WITHDEF], patsubst(translit([withdef_$1], [a-z], [A-Z]), -, _))dnl
AC_SUBST(VAR_WITH)
AC_SUBST(VAR_WITHOUT)
AC_SUBST(VAR_WITHVAL)
AC_SUBST(VAR_WITHDEF)
if test -z "$WITH_VAR" ; then WITH_VAR=`echo ifelse([$2], , no, [$2])` ; fi
if test "$WITH_VAR" != "no"; then
  VAR_WITH=    ; VAR_WITHOUT='#'
  case "$WITH_VAR" in
    [yes)]    VAR_WITHVAL=""
              VAR_WITHDEF="-D""VAR_WITH" ;;
    [*)]      VAR_WITHVAL=WITH_VAR
              VAR_WITHDEF="-D""VAR_WITH="'"'$WITH_VAR'"' ;;
  esac
else
  VAR_WITH='#' ;  VAR_WITHOUT=
  VAR_WITHVAL= ;  VAR_WITHDEF=
fi
popdef([VAR_WITH])dnl
popdef([VAR_WITHOUT])dnl
popdef([VAR_WITHVAL])dnl
popdef([VAR_WITHDEF])dnl
popdef([WITH_VAR])dnl
])

AC_DEFUN([AC_ARG_COND_WITH],
[dnl
AC_ARG_WITH([$1],[$2],[$3],[$4],[$5])
# done with AC_ARG_WITH, now do AC_COND_WITH (rather than AM_CONDITIONAL)
AC_COND_WITH([$1])
])

dnl and the same version as AC_COND_WITH but including the 
dnl AC_DEFINE for WITH_PACKAGE 

AC_DEFUN([AC_COND_WITH_DEFINE],
[dnl the names to be defined...
pushdef([WITH_VAR],    patsubst([with_$1], -, _))dnl
pushdef([VAR_WITH],    patsubst(translit([with_$1], [a-z], [A-Z]), -, _))dnl
pushdef([VAR_WITHOUT], patsubst(translit([without_$1], [a-z], [A-Z]), -, _))dnl
pushdef([VAR_WITHVAL], patsubst(translit([withval_$1], [a-z], [A-Z]), -, _))dnl
pushdef([VAR_WITHDEF], patsubst(translit([withdef_$1], [a-z], [A-Z]), -, _))dnl
AC_SUBST(VAR_WITH)
AC_SUBST(VAR_WITHOUT)
AC_SUBST(VAR_WITHVAL)
AC_SUBST(VAR_WITHDEF)
if test -z "$WITH_VAR" ; then WITH_VAR=`echo ifelse([$2], , no, [$2])` ; fi
if test "$WITH_VAR" != "no"; then
  VAR_WITH=    ; VAR_WITHOUT='#'
  case "$WITH_VAR" in
    [yes)]    VAR_WITHVAL=""
              VAR_WITHDEF="-D""VAR_WITH" ;;
    [*)]      VAR_WITHVAL=WITH_VAR
              VAR_WITHDEF="-D""VAR_WITH="'"'$WITH_VAR'"' ;;
  esac
else
  VAR_WITH='#' ;  VAR_WITHOUT=
  VAR_WITHVAL= ;  VAR_WITHDEF=
fi
if test "_$WITH_VAR" != "_no" ; then
      AC_DEFINE_UNQUOTED(VAR_WITH, "$WITH_VAR", "--with-$1")
fi dnl
popdef([VAR_WITH])dnl
popdef([VAR_WITHOUT])dnl
popdef([VAR_WITHVAL])dnl
popdef([VAR_WITHDEF])dnl
popdef([WITH_VAR])dnl
])