[m-dev.] diff: fix bug with io__write(type_ctor_desc)

[Fergus Henderson]

Estimated hours taken: 1.5

Fix a bug where io__write was crashing with a bus error
if you tried to write out a `type_ctor_desc'.

library/std_util.m:
	Delete the type definition `type_ctor_desc == type_desc',
	since that is wrong -- `type_ctor_desc's for higher-order
	types do not have the same representation as `type_desc's.
	Instead use `type_ctor_desc ---> type_ctor_desc(c_pointer)',
	like we do for `io__state', etc.

library/io.m:
	Treat std_util__type_ctor_desc as a special case in
	io__write, so that we print a proper string for it,
	rather than just printing `type_ctor_desc(<<c_pointer>>)'.

Workspace: /home/pgrad/fjh/ws/hg
Index: library/io.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/io.m,v
retrieving revision 1.216
diff -u -d -r1.216 io.m
--- library/io.m	2000/12/12 14:02:46	1.216
+++ library/io.m	2000/12/21 05:56:47
@@ -1956,6 +1956,8 @@
 		io__write_float(Float)
 	; { univ_to_type(Univ, TypeDesc) } ->
 		io__write_type_desc(TypeDesc)
+	; { univ_to_type(Univ, TypeCtorDesc) } ->
+		io__write_type_ctor_desc(TypeCtorDesc)
 	; { univ_to_type(Univ, OrigUniv) } ->
 		io__write_univ_as_univ(OrigUniv)
 	; { univ_to_type(Univ, C_Pointer) } ->
@@ -2208,6 +2210,21 @@
 
 io__write_type_desc(TypeDesc) -->
 	io__write_string(type_name(TypeDesc)).
+
+:- pred io__write_type_ctor_desc(type_ctor_desc, io__state, io__state).
+:- mode io__write_type_ctor_desc(in, di, uo) is det.
+
+io__write_type_ctor_desc(TypeCtorDesc) -->
+        { type_ctor_name_and_arity(TypeCtorDesc, ModuleName, Name, Arity0) },
+	{ ModuleName = "builtin", Name = "func" ->
+		% The type ctor that we call `builtin:func/N' takes N + 1
+		% type parameters: N arguments plus one return value.
+		% So we need to subtract one from the arity here.
+		Arity = Arity0 - 1
+	;
+		Arity = Arity0
+	},
+	io__format("%s:%s/%d", [s(ModuleName), s(Name), i(Arity)]).
 
 :- pred io__write_univ_as_univ(univ, io__state, io__state).
 :- mode io__write_univ_as_univ(in, di, uo) is det.
Index: library/std_util.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/std_util.m,v
retrieving revision 1.214
diff -u -d -r1.214 std_util.m
--- library/std_util.m	2000/12/18 07:42:53	1.214
+++ library/std_util.m	2000/12/21 06:04:16
@@ -1315,7 +1315,7 @@
 ** tuple, plus one encodes a predicate, plus two encodes a function.
 ** The maximum arity that can be encoded is given by MR_MAX_VARIABLE_ARITY
 ** (see below).
-** The C type corresponding to std_util:type_ctor_desc is `MR_TypeCtorInfo'.
+** The C type corresponding to std_util:type_ctor_desc is `MR_TypeCtorDesc'.
 */
 
 /*
@@ -1441,10 +1441,9 @@
 				             MR_Word arg_type_list);
 ").
 
-	% A type_ctor_desc is really just a subtype of type_desc,
-	% but we hide this from users, since it is an implementation
-	% detail.
-:- type type_ctor_desc == type_desc.
+	% A type_ctor_desc is not (quite) a subtype of type_desc,
+	% so we use a separate type for it.
+:- type type_ctor_desc --> type_ctor_desc(c_pointer).
 
 :- pragma c_code(type_of(_Value::unused) = (TypeInfo::out),
 	will_not_call_mercury, "
-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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