From c5323b292098ece8ba7b3acafbfb87c583202b3f Mon Sep 17 00:00:00 2001
From: Vitor Santos Costa <vsc@dcc.fc.up.pt>
Date: Thu, 12 May 2016 11:42:22 +0100
Subject: [PATCH] undef should not fail immediately: it needs to test for
 exports first

---
 C/absmi.c        |  5 +----
 pl/boot.yap      | 11 ++++++++---
 pl/undefined.yap |  2 +-
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/C/absmi.c b/C/absmi.c
index b4fe32fa2..fe0afb98c 100755
--- a/C/absmi.c
+++ b/C/absmi.c
@@ -888,10 +888,7 @@ static int interrupt_dexecute(USES_REGS1) {
 
 static void undef_goal(USES_REGS1) {
   PredEntry *pe = PredFromDefCode(P);
-  if (Yap_UnknownFlag(CurrentModule) == TermFail) {
-    P = FAILCODE;
-    return;
-  }
+
   BEGD(d0);
 /* avoid trouble with undefined dynamic procedures */
 /* I assume they were not locked beforehand */
diff --git a/pl/boot.yap b/pl/boot.yap
index ff7a8f94c..ea6bb78c9 100644
--- a/pl/boot.yap
+++ b/pl/boot.yap
@@ -273,13 +273,18 @@ private(_).
  '$handle_error'(_Action,_G0,_M0) :- fail.
 
 % cases where we cannot afford to ever fail.
-'$undefp'([_|print_message(Context, Msg)], true) :- !,
+'$undefp'([ImportingMod|G], _) :- !,
+	recorded('$import','$import'(ExportingModI,ImportingMod,G,G0I,_,_),_), !,
+ % writeln('$execute0'(G0I, ExportingModI)),
+	'$execute0'(G0I, ExportingModI).
+'$undefp'([_|print_message(Context, Msg)], _) :- !,
     '$early_print_message'(Context, Msg).
 % undef handler
 '$undefp'([M0|G0], Action) :-
     % make sure we do not loop on undefined predicates
     '$stop_creeping'(Current),
     yap_flag( unknown, Action, fail),
+    Action\=fail,
  %   yap_flag( debug, Debug, false),
     (
      '$undefp_search'(M0:G0, NM:NG),
@@ -419,7 +424,7 @@ true :- true.
     % simple trick to find out if this is we are booting from Prolog.
     % boot from a saved state
     (
-     current_prolog_flag(saved_program, false)	
+     current_prolog_flag(saved_program, false)
     ->
      prolog_flag(verbose, OldV, silent),
      prolog_flag(resource_database, RootPath),
@@ -1387,7 +1392,7 @@ not(G) :-    \+ '$execute'(G).
     bootstrap( F ),
     yap_flag(verbose, _, Old),
     '$live'.
-    
+
 
 bootstrap(F) :-
 %	'$open'(F, '$csult', Stream, 0, 0, F),
diff --git a/pl/undefined.yap b/pl/undefined.yap
index 45cedfaa6..48bde51a6 100644
--- a/pl/undefined.yap
+++ b/pl/undefined.yap
@@ -82,7 +82,7 @@ followed by the failure of that call.
 :- '$set_no_trace'('$handle_error'(_,_,_), prolog).
 
 /**
-Z * @pred '$undefp_expand'(+ M0:G0, -MG)
+ * @pred '$undefp_expand'(+ M0:G0, -MG)
  *
  * @param G0 input goal
  * @param M0 current module