diff: fix var.m mode errors (`any' inst in higher-order term)

[Fergus Henderson]

extras/trailed_update/var.m:
	Avoid mode errors in debug_freeze/{3,4} which were caused by the use
	of a variable of inst `any' as the curried argument in a higher-order
	term.  The fix was to replace `unsafe_perform_io(dump_var(Var))'
	with `unsafe_dump_var(Var)' where unsafe_dump_var/1 is a new impure
	version of dump_var/3.
	(The mode errors were detected as a result of Andrew Bromage's
	recent change to fix mode checking for lambda expressions.
	In this particular case, as it happens, there is no genuine error,
	becaused dump_var/1 does not instantiate its argument.
	However, there's no way for the mode checker to know that,
	so it is correct to report an error.)

Index: var.m
===================================================================
RCS file: /home/mercury1/repository/mercury/extras/trailed_update/var.m,v
retrieving revision 1.9
diff -u -u -r1.9 var.m
--- var.m	1997/12/11 21:23:27	1.9
+++ var.m	1998/02/14 14:56:01
@@ -97,6 +97,9 @@
 	% dump_var prints out a representation of a variable.
 :- pred dump_var(var(T)::in(any), io__state::di, io__state::uo) is cc_multi.
 
+	% unsafe_dump_var/1: an impure version of dump_var/3.
+:- impure pred unsafe_dump_var(var(T)::in(any)) is det.
+
 	% var__is_ground/2 can be used to test if a variable is ground.
 	%
 	% Declaratively, is_ground(Var, Result) is true iff
@@ -922,7 +925,7 @@
 		impure unsafe_perform_io(print("freezing: ")),
 		impure unsafe_perform_io(print(Msg)),
 		impure unsafe_perform_io(print(": ")),
-		impure unsafe_perform_io(dump_var(Var)),
+		impure unsafe_dump_var(Var),
 		impure unsafe_perform_io(nl),
 
 		freeze(Var, debug_pred(Msg, Pred)),
@@ -930,13 +933,13 @@
 		impure unsafe_perform_io(print("frozen: ")),
 		impure unsafe_perform_io(print(Msg)),
 		impure unsafe_perform_io(print(": ")),
-		impure unsafe_perform_io(dump_var(Var)),
+		impure unsafe_dump_var(Var),
 		impure unsafe_perform_io(nl)
 	;
 		impure unsafe_perform_io(print("freeze failed: ")),
 		impure unsafe_perform_io(print(Msg)),
 		impure unsafe_perform_io(print(": ")),
-		impure unsafe_perform_io(dump_var(Var)),
+		impure unsafe_dump_var(Var),
 		impure unsafe_perform_io(nl),
 		fail
 	).
@@ -949,7 +952,7 @@
 		impure unsafe_perform_io(print("freezing: ")),
 		impure unsafe_perform_io(print(Msg)),
 		impure unsafe_perform_io(print(": ")),
-		impure unsafe_perform_io(dump_var(X)),
+		impure unsafe_dump_var(X),
 		impure unsafe_perform_io(nl),
 
 		freeze(X, debug_pred2(Msg, Pred), Y),
@@ -957,13 +960,13 @@
 		impure unsafe_perform_io(print("frozen: ")),
 		impure unsafe_perform_io(print(Msg)),
 		impure unsafe_perform_io(print(": ")),
-		impure unsafe_perform_io(dump_var(X)),
+		impure unsafe_dump_var(X),
 		impure unsafe_perform_io(nl)
 	;
 		impure unsafe_perform_io(print("freeze failed: ")),
 		impure unsafe_perform_io(print(Msg)),
 		impure unsafe_perform_io(print(": ")),
-		impure unsafe_perform_io(dump_var(X)),
+		impure unsafe_dump_var(X),
 		impure unsafe_perform_io(nl),
 		fail
 	).
@@ -1021,6 +1024,10 @@
 :- pragma c_code(dump_var(Var::in(any), IO0::di, IO::uo), may_call_mercury, "
 	ML_var_print(TypeInfo_for_T, Var);
 	IO = IO0;
+").
+
+:- pragma c_code(unsafe_dump_var(Var::in(any)), may_call_mercury, "
+	ML_var_print(TypeInfo_for_T, Var);
 ").
 
 :- pred dump_var_rep(var_rep(T)::in(var_rep_any),
-- 
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.