+# check for pgrep
+AC_PATH_PROG([PGREP], [pgrep], [no])
+AM_CONDITIONAL([HAVE_PGREP], [test "x$PGREP" != "xno"])
+
+# set $IN_GIT_REPO if we're in the Git repository; the `bootstrap` file
+# is not distributed in tarballs
+AS_IF([test -f "$srcdir/bootstrap"], [in_git_repo=yes], [in_git_repo=no])
+AM_CONDITIONAL([IN_GIT_REPO], [test "x$in_git_repo" = "xyes"])
+
+# check for bison
+AC_PROG_YACC
+BISON=$YACC
+AX_PROG_BISON_VERSION([2.4], [have_bison=yes])
+
+AS_IF([test "x$have_bison" != "xyes"], [
+ AS_IF([test "x$in_git_repo" = "xyes"], [
+ AC_MSG_FAILURE([
+Bison >= 2.4 is required when building from the Git repository. You can
+set the YACC variable to override automatic detection.
+ ])
+ ], [
+ AC_MSG_WARN([
+Missing Bison >= 2.4. Note that the parser files are already built in
+this distribution tarball, so Bison is only needed if you intend to
+modify their sources. You can set the YACC variable to override automatic
+detection.
+ ])
+ ])
+])
+AM_CONDITIONAL([HAVE_BISON], [test "x$have_bison" = "xyes"])
+
+# check for flex
+AC_PROG_LEX
+FLEX=$LEX
+AX_PROG_FLEX_VERSION([2.5.35], [have_flex=yes])
+
+AS_IF([test "x$have_flex" != "xyes"], [
+ AS_IF([test "x$in_git_repo" = "xyes"], [
+ AC_MSG_FAILURE([
+Flex >= 2.5.35 is required when building from the Git repository. You can
+set the LEX variable to override automatic detection.
+ ])
+ ], [
+ AC_MSG_WARN([
+Missing Flex >= 2.5.35. Note that the lexer files are already built in
+this distribution tarball, so Flex is only needed if you intend to
+modify their sources. You can set the LEX variable to override automatic
+detection.
+ ])
+ ])
+])
+AM_CONDITIONAL([HAVE_FLEX], [test "x$have_flex" = "xyes"])
+
+