configure: Fix checking of missing programs

diff --git a/configure.ac b/configure.ac
index ef0c7a1..bf57ebb 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -51,17 +51,20 @@ if test "x$OCAMLLEX" = "xno"; then
     AC_MSG_ERROR([OCaml ocamllex lexical generator tool is required])
 fi
 
-AC_CHECK_PROG(MENHIR, [menhir], [menhir], [
+AC_CHECK_PROG([MENHIR], [menhir], [menhir], [no])
+if test "x$MENHIR" = "xno"; then
     AC_MSG_ERROR([OCaml menhir parser generator is required])
-])
+fi
 
-AC_CHECK_PROG([POD2MAN], [pod2man], [pod2man], [
+AC_CHECK_PROG([POD2MAN], [pod2man], [pod2man], [no])
+if test "x$POD2MAN" = "xno"; then
     AC_MSG_ERROR([pod2man tool from Perl is required])
-])
+fi
 
-AC_CHECK_PROG([POD2TEXT], [pod2text], [pod2text], [
+AC_CHECK_PROG([POD2TEXT], [pod2text], [pod2text], [no])
+if test "x$POD2TEXT" = "xno"; then
     AC_MSG_ERROR([pod2text tool from Perl is required])
-])
+fi
 
 dnl Substitute OCaml flags and packages.
 AC_SUBST([OCAMLFLAGS], ["-g -safe-string -warn-error +C+D+E+F+L+M+P+S+U+V+Y+Z+X+52-3"])