diff: polymorphic abstract exported eqv types error

[Fergus Henderson]

Estimated hours taken: 1

compiler/make_hlds.m:
	Print out a "Sorry, not implemented" message for
	abstract exported polymorphic equivalence types
	whose bodies have fewer type variables than their
	heads.  (Previously the compiler allow this,
	but generated code that dumped core.)

Index: make_hlds.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/make_hlds.m,v
retrieving revision 1.255
diff -u -u -r1.255 make_hlds.m
--- make_hlds.m	1998/01/25 07:47:04	1.255
+++ make_hlds.m	1998/01/27 15:01:32
@@ -936,6 +936,40 @@
 	"Warning: undiscriminated union types (`+') not implemented.\n"),
 			io__set_output_stream(OldStream, _)
 		;
+			% XXX we can't handle abstract exported
+			% polymorphic equivalence types with monomorphic
+			% bodies, because the compiler stuffs up the
+			% type_info handling -- the caller passes type_infos,
+			% but the callee expects no type_infos
+			{ Body = eqv_type(EqvType) },
+			{ Status = abstract_exported },
+			{ term__contains_var_list(Args, Var) },
+			{ \+ term__contains_var(EqvType, Var) }
+		->
+			io__stderr_stream(StdErr),
+			io__set_output_stream(StdErr, OldStream),
+			prog_out__write_context(Context),
+			io__write_string(
+	"Sorry, not implemented: polymorphic equivalence type,\n"),
+			prog_out__write_context(Context),
+			io__write_string(
+	"  with monomorphic definition, exported as abstract type.\n"),
+			globals__io_lookup_bool_option(verbose_errors,
+				VerboseErrors),
+			( { VerboseErrors = yes } ->
+				io__write_strings([
+	"\tA quick work-around is just export the type as a concrete type,\n",
+	"\tby putting the type definition in the interface section.\n",
+	"\tA better work-around is to use a \"wrapper\" type, with just one\n",
+	"\tfunctor that has just one arg, instead of an equivalence type.\n",
+	"\t(There's no performance penalty for this -- the compiler will\n",
+	"\toptimize the wrapper away.)\n"])
+			;
+				[]
+			),
+			io__set_exit_status(1),
+			io__set_output_stream(OldStream, _)
+		;
 			[]
 		)
 	).
-- 
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.