AC_LANG([C++])

old_CPPFLAGS="$CPPFLAGS"
old_LIBS="$LIBS"
CPPFLAGS="-I$nix/include/nix"
LIBS="-L$nix/lib/nix"
AC_CHECK_HEADER([store-api.hh], [:],
  [AC_MSG_ERROR([Nix headers not found; please install Nix or check the `--with-nix' option.])])
AC_CHECK_LIB([expr], [_ZN3nix17parseExprFromFileERNS_9EvalStateESs], [:],
  [AC_MSG_ERROR([Nix library not found; please install Nix or check the `--with-nix' option.])])
CPPFLAGS="$old_CPPFLAGS"
LIBS="$old_LIBS"