diff: report error for mixing tabling & trailing

[Fergus Henderson]

library/private_builtin.m:
	Ensure that tabling will report a "sorry, not implemented"
	error if used in a grade with trailing.  This is necessary
	because the code that would be needed to save and restore
	the trail state has not been implemented.
	Also use `\\' instead of `\' for macro line continuations
	inside pragma c_code, so that the generated C code doesn't
	contain very long lines (and so that the `#line' directives
	work properly).

doc/reference_manual.texi:
	Document that with the current implementation, trailing
	does not work in all compilation grades.

Index: doc/reference_manual.texi
===================================================================
RCS file: /home/mercury1/repository/mercury/doc/reference_manual.texi,v
retrieving revision 1.99
diff -u -r1.99 reference_manual.texi
--- reference_manual.texi	1998/07/16 02:44:11	1.99
+++ reference_manual.texi	1998/07/26 15:07:48
@@ -3310,7 +3310,7 @@
 semantics.  If the @samp{io__state} arguments were
 left off, then the Mercury implementation might apply
 undesirable optimizations (e.g. reordering, duplicate
-call elimination, tabling, lazy evaluation...)
+call elimination, tabling, lazy evaluation, @dots{})
 to this procedure, which could effect the behaviour
 of the program in unpredictable ways.
 
@@ -4306,6 +4306,15 @@
 This ensures that code which does not use tabling does not pay any
 runtime overheads from the more complicated execution mechanism
 required by (minimal model) tabling.
+
+ at strong{Please note:}
+the current implementation of tabling does not support all the
+possible compilation grades (see the "Compilation model options"
+section of the Mercury User's Guide) allowed by the Mercury
+implementation.  In particular, if you enable the use of trailing,
+or if you select a garbage collection method other than the default
+(conservative), then any use of tabling will result in a
+``Sorry, not implemented'' error at runtime.
 
 @node Termination analysis
 @subsection Termination analysis
Index: library/private_builtin.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/private_builtin.m,v
retrieving revision 1.2
diff -u -r1.2 private_builtin.m
--- private_builtin.m	1998/05/27 14:46:19	1.2
+++ private_builtin.m	1998/07/26 15:13:22
@@ -937,33 +937,33 @@
 
 ResumeStackNode** ML_resumption_stack = NULL;
 
-#define ML_RESUME_PUSH()						\
-	do {								\
-		++ML_resumption_sp;					\
-		if (ML_resumption_sp >= ML_resumption_stack_size ||	\
-				ML_resumption_stack == NULL) 		\
-		{							\
-			ML_resumption_stack_size =			\
-				ML_resumption_stack_size*2;		\
-			ML_resumption_stack = table_reallocate(		\
-				ML_resumption_stack,			\
-				ML_resumption_stack_size*sizeof(	\
-					ResumeStackNode*));		\
-		}							\
-		ML_resumption_stack[ML_resumption_sp] = table_allocate(	\
-			sizeof(ResumeStackNode));			\
+#define ML_RESUME_PUSH()						\\
+	do {								\\
+		++ML_resumption_sp;					\\
+		if (ML_resumption_sp >= ML_resumption_stack_size ||	\\
+				ML_resumption_stack == NULL) 		\\
+		{							\\
+			ML_resumption_stack_size =			\\
+				ML_resumption_stack_size*2;		\\
+			ML_resumption_stack = table_reallocate(		\\
+				ML_resumption_stack,			\\
+				ML_resumption_stack_size*sizeof(	\\
+					ResumeStackNode*));		\\
+		}							\\
+		ML_resumption_stack[ML_resumption_sp] = table_allocate(	\\
+			sizeof(ResumeStackNode));			\\
 	} while (0)
 	
-#define ML_RESUME_POP()							\
-	do {								\
-		if (ML_resumption_sp < 0) {				\
-			fatal_error(""resumption stack underflow"");	\
-		}							\
-		table_free(ML_resumption_stack[ML_resumption_sp]);	\
-		--ML_resumption_sp;					\
+#define ML_RESUME_POP()							\\
+	do {								\\
+		if (ML_resumption_sp < 0) {				\\
+			fatal_error(""resumption stack underflow"");	\\
+		}							\\
+		table_free(ML_resumption_stack[ML_resumption_sp]);	\\
+		--ML_resumption_sp;					\\
 	} while (0)
 
-#define ML_RESUME_VAR							\
+#define ML_RESUME_VAR							\\
 	ML_resumption_stack[ML_resumption_sp]
 
 /*
@@ -1036,6 +1036,15 @@
 	ML_RESUME_VAR->s_p = MR_sp;
 	ML_RESUME_VAR->cur_fr = MR_curfr;
 	ML_RESUME_VAR->max_fr = MR_maxfr;
+
+#ifdef MR_USE_TRAIL
+	/*
+	** We ought to save the trail state here --
+	** this is not yet implemented.
+	*/
+	MR_fatal_error(""Sorry, not implemented: ""
+		""can't have both tabling and trailing"");
+#endif
 
 	ML_RESUME_VAR->changed = 1;
 	

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3        |     -- the last words of T. S. Garp.