allow setting up arithmetic exception handling.

C/init.c

@@ -954,6 +954,7 @@ InitFlags(void)
   /* note that Yap_heap_regs must be set first */
 
   yap_flags[LANGUAGE_MODE_FLAG] = 0;
+  yap_flags[FLOATING_POINT_EXCEPTION_MODE_FLAG] = TRUE;
   yap_flags[SOURCE_MODE_FLAG] = FALSE;
   yap_flags[WRITE_QUOTED_STRING_FLAG] = FALSE;
   /* we do not garantee safe assert in parallel mode */

C/stdpreds.c

@@ -1638,6 +1638,11 @@ p_set_yap_flags( USES_REGS1 )
       return(FALSE);
     yap_flags[SOURCE_MODE_FLAG] = value;
     break;
+  case FLOATING_POINT_EXCEPTION_MODE_FLAG:
+    if (value != 0 && value !=  1)
+      return(FALSE);
+    yap_flags[FLOATING_POINT_EXCEPTION_MODE_FLAG] = value;
+    break;
   case WRITE_QUOTED_STRING_FLAG:
     if (value != 0 && value !=  1)
       return(FALSE);

C/sysbits.c

@@ -1422,7 +1422,7 @@ Yap_MathException__( USES_REGS1 )
   int raised;
 
 #if HAVE_FETESTEXCEPT
-#pragma STDC FENV_ACCESS ON
+  // #pragma STDC FENV_ACCESS ON
   if ((raised = fetestexcept( FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)) ) {
 
 	feclearexcept(FE_ALL_EXCEPT);

H/Yap.h

@@ -391,6 +391,7 @@ typedef enum
 {
   LANGUAGE_MODE_FLAG = 8,
   SOURCE_MODE_FLAG = 11,
+  FLOATING_POINT_EXCEPTION_MODE_FLAG = 12,
   WRITE_QUOTED_STRING_FLAG = 13,
   ALLOW_ASSERTING_STATIC_FLAG = 14,
   HALT_AFTER_CONSULT_FLAG = 15,
@@ -680,7 +681,7 @@ typedef struct thread_mbox {
     Term name;
     pthread_mutex_t mutex;
     pthread_cond_t cond;
-    struct idb_queue msgs;
+   struct idb_queue msgs;
     int  nmsgs, nclients;  // if nclients < 0 mailbox has been closed.
     bool open;
     struct thread_mbox *next;

H/eval.h

@@ -396,7 +396,9 @@ Yap_FoundArithError__(USES_REGS1)
 { 
   if (LOCAL_Error_TYPE != YAP_NO_ERROR)
     return LOCAL_Error_TYPE;
-  return Yap_MathException();
+  if (yap_flags[FLOATING_POINT_EXCEPTION_MODE_FLAG]) // test support for exception
+    return Yap_MathException();
+  return YAP_NO_ERROR;
 }
 
 Atom Yap_NameOfUnaryOp(int i);

packages/CLPBN/clpbn.yap

@@ -29,6 +29,8 @@
 
 :- use_module(library(maplist)).
 
+:- yap_flag(arithmetic_exceptions,false).
+
 :- attribute key/1, dist/2, evidence/1.
 
 :- use_module('clpbn/ve',

packages/ProbLog/problog/os.yap

@@ -1,4 +1,4 @@
-%%% -*- Mode: Prolog; -*-
+<%%% -*- Mode: Prolog; -*-
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %
@@ -221,6 +221,7 @@
 % load library modules
 :- use_module(library(system), [exec/3, file_exists/1,wait/2]).
 :- use_module(library(lists), [memberchk/2]).
+:- yap_flag(arithmetic_exceptions, false).
 
 % load our own modules
 :- use_module(gflags, _, [flag_get/2]).

pl/flags.yap

@@ -67,7 +67,26 @@ opportunity. Initial value is 10,000. May be changed. A value of 0
     Read-write flag telling a suffix for files associated to Prolog
 sources. It is `yap` by default.
 
-+ `bounded is iso `
++ `arithmetic_exceptions `
+
+    Read-write flag telling whether arithmetic exceptions generate
+    Prolog exceptions. If enabled:
+
+~~~~
+ ?- X is 2/0.
+     ERROR!!
+     ZERO DIVISOR ERROR- X is Exp
+~~~~
+
+    If disabled:
+~~~~
+ ?- X is 2/0.
+X = (+inf).
+~~~~
+
+    It is `true` by default, but it is disabled by packages like CLP(BN) and ProbLog.
+
++ `bounded` is iso
 
     Read-only flag telling whether integers are bounded. The value depends
 on whether YAP uses the GMP library or not.
@@ -955,6 +974,19 @@ yap_flag(write_strings,off) :- !,
 yap_flag(write_strings,X) :-
 	'$do_error'(domain_error(flag_value,write_strings+X),yap_flag(write_strings,X)).
 
+yap_flag(arithmetic_exceptions,OUT) :-
+	var(OUT), !,
+	'$access_yap_flags'(12,X),
+	'$transl_to_true_false'(X,OUT).
+yap_flag(arithmetic_exceptions,true) :- !,
+	'$transl_to_true_false'(X,true),
+	'$set_yap_flags'(12,X).
+yap_flag(arithmetic_exceptions,false) :- !,
+	'$transl_to_true_false'(X,false),
+	'$set_yap_flags'(12,X).
+yap_flag(arithmetic_exceptions,X) :-
+	'$do_error'(domain_error(flag_value,arithmetic_exceptions+X),yap_flag(arithmetic_exceptions,[true,false])).
+
 yap_flag(prompt_alternatives_on,OUT) :-
 	var(OUT), !,
 	'$prompt_alternatives_on'(OUT).
@@ -1085,6 +1117,7 @@ yap_flag(max_threads,X) :-
 	\+ '$undefined'(reset_op_counters, prolog).
 
 '$yap_system_flag'(agc_margin).
+'$yap_system_flag'(arithmetic_exceptions).
 '$yap_system_flag'(chr_toplevel_show_store).
 '$yap_system_flag'(debugger_print_options).
 '$yap_system_flag'(discontiguous_warnings).