diff: passes_aux.m polymorphism problem

[Fergus Henderson]

Hi,

Zoltan, can you please review this one?

Fix a bunch of warnings about unbound type variables in mercury_compile.m.

compiler/passes_aux.m:
	Change the type `task(T)' to just plain `task', and change
	`update_module_cookie' to use `univ' for the cookie type,
	rather than `T'.  Add some comments explaining this.

Index: passes_aux.m
===================================================================
RCS file: /home/staff/zs/imp/mercury/compiler/passes_aux.m,v
retrieving revision 1.19
diff -u -r1.19 passes_aux.m
--- passes_aux.m	1997/06/11 09:00:07	1.19
+++ passes_aux.m	1997/06/13 08:18:00
@@ -18,7 +18,7 @@
 
 %-----------------------------------------------------------------------------%
 
-:- type task(T)	--->	update_proc(pred(
+:- type task	--->	update_proc(pred(
 				proc_info, module_info, proc_info))
 		;	update_proc_io(pred(
 				pred_id, proc_id, module_info,
@@ -34,10 +34,43 @@
 				pred_id, proc_id, proc_info, proc_info,
 				module_info, module_info,
 				io__state, io__state))
+		% It would be better to use an existentiallly-quantified type
+		% rather than `univ' here, but Mercury 0.6 doesn't support
+		% existentially-quantified types.
 		;	update_module_cookie(pred(
 				pred_id, proc_id, proc_info, proc_info,
+				univ, univ, module_info, module_info),
+				univ)
+		.
+
+/****************
+
+Note that update_module_cookie causes some difficulties.
+Ideally, it should be implemented using existential types:
+
+	:- type task --->
+			...
+		;	some [T] update_module_cookie(pred(
+				pred_id, proc_id, proc_info, proc_info,
 				T, T, module_info, module_info),
-				T).
+				T)
+
+That would avoid the need for messing about with type_to_univ and
+univ_to_type.
+
+Originally, it was implemented by changing `task' to `task(T)':
+
+	:- type task(T) --->
+			...
+		;	update_module_cookie(pred(
+				pred_id, proc_id, proc_info, proc_info,
+				T, T, module_info, module_info),
+				T)
+
+but that is not a good solution, because it causes a lot of warnings
+about unbound type variables.
+
+****************/
 
 :- inst task =	bound(( update_proc(pred(in, in, out) is det)
 		;	update_proc_io(pred(in, in, in, in, out, di, uo) is det)
@@ -52,11 +85,11 @@
 
 :- mode task ::	task -> task.
 
-:- pred process_all_nonimported_procs(task(T), module_info, module_info,
+:- pred process_all_nonimported_procs(task, module_info, module_info,
 	io__state, io__state).
 :- mode process_all_nonimported_procs(task, in, out, di, uo) is det.
 
-:- pred process_all_nonimported_procs(task(T), task(T),
+:- pred process_all_nonimported_procs(task, task,
 	module_info, module_info, io__state, io__state).
 :- mode process_all_nonimported_procs(task, out(task), in, out, di, uo) is det.
 
@@ -108,7 +141,7 @@
 	process_nonimported_procs_in_preds(PredIds, Task0, Task,
 		ModuleInfo0, ModuleInfo).
 
-:- pred process_nonimported_procs_in_preds(list(pred_id), task(T), task(T),
+:- pred process_nonimported_procs_in_preds(list(pred_id), task, task,
 	module_info, module_info, io__state, io__state).
 :- mode process_nonimported_procs_in_preds(in, task, out(task), in, out,
 	di, uo) is det.
@@ -125,7 +158,7 @@
 	process_nonimported_procs_in_preds(PredIds, Task1, Task,
 		ModuleInfo1, ModuleInfo).
 
-:- pred process_nonimported_procs(list(proc_id), pred_id, task(T), task(T),
+:- pred process_nonimported_procs(list(proc_id), pred_id, task, task,
 	module_info, module_info, io__state, io__state).
 :- mode process_nonimported_procs(in, in, task, out(task), in, out, di, uo)
 	is det.

-- 
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.