[m-dev.] for review: allow separate mode decls for zero arity preds

[Fergus Henderson]

On 30-Aug-1999, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> 
> Allow separate mode declarations for predicates with no arguments
> (previously they were considered to be duplicate mode declarations).
> This avoids the need to special case such predicates when writing
> out declarations for inter-module optimization. 
> 
> If there is no mode declaration and the `:- pred' declaration does
> not include the determinism, a default mode `:- mode foo.' is added.

What about the case where there is no mode declaration and no pred
declaration either?

In that case, your code adds a default mode.
This is a change from the previous behaviour, and I'm not convinced
that it is the right thing to do.  It also happens to break
extras/clpr/samples/tests.m.

In cases where there is no mode declaration and no pred declaration,
the default mode will be inferred if it is used.  But if it is not used,
I do not think there is any complelling reason why it should be added.

Therefore I propose the following fix.

----------

Estimated hours taken: 0.75

compiler/make_hlds.m:
	Don't add a default mode for predicates with zero arity
	and no pred or mode declaration.  The rationale is that
	there's no compelling reason to add a default mode, since
	the mode will be inferred anyway, if it is used,
	and adding a default mode breaks some existing code,
	e.g. extras/clpr/samples/tests.m, which assumes that
	a predicate that is not called and which has zero arity and
	no pred or mode declaration need not be mode-correct.

Workspace: /usr/hg/public/test_mercury/test_dirs/hg/mercury
Index: compiler/make_hlds.m
===================================================================
RCS file: /home/staff/zs/imp/mercury/compiler/make_hlds.m,v
retrieving revision 1.301
diff -u -r1.301 make_hlds.m
--- compiler/make_hlds.m	1999/08/31 05:25:33	1.301
+++ compiler/make_hlds.m	1999/09/03 15:22:53
@@ -2943,13 +2943,13 @@
 		{ ModuleInfo = ModuleInfo0 },
 		{ Info = Info0 }
 	;
-		{ pred_info_clauses_info(PredInfo1, Clauses0) },
-		{ pred_info_typevarset(PredInfo1, TVarSet0) },
-		{ maybe_add_default_func_mode(PredInfo1, PredInfo2a, _) },
-		maybe_add_default_zero_arity_pred_mode(PredInfo2a,
-			PredInfo2, _),
-		{ pred_info_procedures(PredInfo2, Procs) },
-		{ map__keys(Procs, ModeIds) },
+		{
+		pred_info_clauses_info(PredInfo1, Clauses0),
+		pred_info_typevarset(PredInfo1, TVarSet0),
+		maybe_add_default_func_mode(PredInfo1, PredInfo2, _),
+		pred_info_procedures(PredInfo2, Procs),
+		map__keys(Procs, ModeIds)
+		},
 		clauses_info_add_clause(Clauses0, PredId, ModeIds,
 			ClauseVarSet, TVarSet0, Args, Body, Context,
 			IsAssertion, Goal,

-- 
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.
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