[m-rev.] diff: support get_functor of existential types in erlang

[Peter Wang]

[I won't commit this until the repository is back in order]

Estimated hours taken: 4
Branches: main

library/erlang_rtti_implementation.m:
	Make `get_functor_with_names' able to succeed on existential types.

	Make `eval_pseudo_type_info_thunk' not subtract 512 from the variable
	number of existential type variables, to be consistent with the C
	backends.  Do the subtraction only when we're using the variable
	number as an index, in `exist_type_info'.

	Rename `type_info/2' to `concrete_type_info' to reduce confusion.


Index: library/erlang_rtti_implementation.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/library/erlang_rtti_implementation.m,v
retrieving revision 1.25
diff -u -b -r1.25 erlang_rtti_implementation.m
--- library/erlang_rtti_implementation.m	18 Sep 2007 07:56:35 -0000	1.25
+++ library/erlang_rtti_implementation.m	20 Sep 2007 06:59:12 -0000
@@ -1027,7 +1027,7 @@
 
     MaybePTI = ArgInfo ^ du_arg_type,
     Info = yes({TypeInfo, yes({Functor, Term})}),
-    ArgTypeInfo = type_info(Info, MaybePTI),
+    ArgTypeInfo = concrete_type_info(Info, MaybePTI),
 
     SubTerm = get_subterm(ArgTypeInfo, Term, Loc, extra_args(Functor) + 1),
     Univ = univ(SubTerm).
@@ -1061,7 +1061,7 @@
         PtiInfo = no : pti_info(int),
         TiInfo = yes({TypeInfo0, PtiInfo}),
         EqvType = TypeCtorInfo0 ^ type_ctor_eqv_type,
-        TypeInfo1 = type_info(TiInfo, EqvType),
+        TypeInfo1 = concrete_type_info(TiInfo, EqvType),
         TypeInfo = collapse_equivalences(TypeInfo1)
     ;
         TypeInfo = TypeInfo0
@@ -1216,19 +1216,13 @@
         TypeCtorRep = etcr_du,
         FunctorReps = TypeCtorInfo ^ type_ctor_functors,
         ( matching_du_functor_number(FunctorReps, NumFunctor, FunctorRep) ->
-            MaybeExistInfo = FunctorRep ^ edu_exist_info,
-            (
-                MaybeExistInfo = yes(_),
-                Result = no
-            ;
-                MaybeExistInfo = no,
                 ArgInfos = FunctorRep ^ edu_arg_infos,
 
                 list.map2(
                     (pred(ArgInfo::in, ArgTypeInfo::out, ArgName::out) is det :-
                         MaybePTI = ArgInfo ^ du_arg_type,
                         Info = yes({TypeInfo, no : pti_info(int)}),
-                        ArgTypeInfo = type_info(Info, MaybePTI),
+                    ArgTypeInfo = concrete_type_info(Info, MaybePTI),
                         
                         MaybeArgName = ArgInfo ^ du_arg_name,
                         (
@@ -1243,7 +1237,6 @@
                 Name = string.from_char_list(FunctorRep ^ edu_name),
                 Arity = FunctorRep ^ edu_orig_arity,
                 Result = yes({Name, Arity, ArgTypes, ArgNames})
-            )
         ;
             Result = no
         )
@@ -2172,9 +2165,9 @@
     % Given a plain or pseudo type_info, return the concrete type_info
     % which represents the type.
     %
-:- func type_info(ti_info(T), maybe_pseudo_type_info) = type_info.
+:- func concrete_type_info(ti_info(T), maybe_pseudo_type_info) = type_info.
 
-type_info(Info, MaybePTI) = TypeInfo :-
+concrete_type_info(Info, MaybePTI) = TypeInfo :-
     (
         MaybePTI = pseudo(PseudoThunk),
         (
@@ -2205,7 +2198,9 @@
             TypeInfo = exist_type_info(ParentTypeInfo, Functor, Term, N)
         ;
             MaybeFunctorAndTerm = no,
-            error("eval_pseudo_type_info requires a functor rep")
+            % If we don't have the term available then leave the existential
+            % type variables in place, e.g. for get_functor_with_names.
+            TypeInfo = unsafe_cast(N)
         )
     ;
         EvalResult = pseudo_type_info(PseudoTypeInfo),
@@ -2219,7 +2214,8 @@
     MaybeExist = Functor ^ edu_exist_info,
     (
         MaybeExist = yes(ExistInfo),
-        ExistLocn = list.index1_det(ExistInfo ^ exist_typeinfo_locns, N),
+        % The first existential type variable is numbered 512.
+        ExistLocn = list.index1_det(ExistInfo ^ exist_typeinfo_locns, N - 512),
         (
             ExistLocn = plain_typeinfo(X),
 
@@ -2280,13 +2276,13 @@
 
 var_arity_arg_type_info(Info, TypeInfo, Index) = ArgTypeInfo :-
     MaybePTI = TypeInfo ^ var_arity_pseudo_type_info_index(Index),
-    ArgTypeInfo = type_info(Info, MaybePTI).
+    ArgTypeInfo = concrete_type_info(Info, MaybePTI).
 
 :- func arg_type_info(ti_info(T), TypeInfo, int) = type_info.
 
 arg_type_info(Info, TypeInfo, Index) = ArgTypeInfo :-
     MaybePTI = TypeInfo ^ pseudo_type_info_index(Index),
-    ArgTypeInfo = type_info(Info, MaybePTI).
+    ArgTypeInfo = concrete_type_info(Info, MaybePTI).
 
 %-----------------------------------------------------------------------------%
 
@@ -2413,7 +2409,9 @@
             is_integer(MaybeTypeInfo), MaybeTypeInfo < 512 ->
                 { universal_type_info, MaybeTypeInfo };
             is_integer(MaybeTypeInfo) ->
-                { existential_type_info, MaybeTypeInfo - 512 };
+                % We don't subtract 512 here so that the test output will be
+                % the same as for the C backends.
+                { existential_type_info, MaybeTypeInfo };
             true ->
                 { pseudo_type_info, MaybeTypeInfo }
         end,

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