-# Can we rebuild the parsers?
-# We really want flex and refuse other lex. So, the parser is portable and
-# does not induce extra lib dependency
-AC_PROG_LEX
-if test "$LEX" != flex; then
- LEX="$SHELL $missing_dir/missing flex"
+if test "x$with_context" = "xpthread"; then
+ AC_CHECK_HEADERS([pthread.h])
+ AC_CHECK_LIB(pthread,pthread_create,,
+ [AC_MSG_ERROR([[Cannot find pthreads, no way (try --with-context=ucontext if you haven't already tried).]])])
+ AC_DEFINE([USE_PTHREADS],1,[Define if we use pthreads or not])
+ AC_MSG_RESULT(You have pthreads. Let's use them.)
+fi
+
+dnl #
+dnl # 4. determine a few additional details
+dnl #
+
+if test "x$with_context" = "xucontext" ; then
+dnl # direction of stack grow
+ AC_CHECK_STACKGROWTH(PTH_STACKGROWTH)
+ if test ".$ac_cv_check_stackgrowth" = ".down"; then
+ PTH_STACK_GROWTH="down"
+ else
+ PTH_STACK_GROWTH="up"
+ fi
+ AC_SUBST(PTH_STACK_GROWTH)
+
+ AC_CHECK_STACKSETUP(makecontext, pth_skaddr_makecontext, pth_sksize_makecontext)