!ASIS Issue #066
!topic Root and universal types in ASIS
!reference  ASIS 95-16.7, 3.11.13
!from Sergey Rybin
!keywords A_Root_Type_Definition Corresponding_Root_Type semantic queries
!discussion

What should be returned by Asis.Definitions.Corresponding_Root_Type
(its definition is appended to this comment) in the following
situation:

type My_Int is range -100 .. 100;

type My_New_Int is new My_Int;
                   ^^^^^^^^^^^
                       |

                      Elem

What should be the result of Corresponding_Root_Type (Elem): the
declaration of My_Int or the artificial declaration of the
root_integer type?

RM95 3.5.4 (14) says:

   A type defined by an integer_type_definition is implicitly derived
   from root_integer, an anonymous predefined (specific) integer
   type, whose base range is System.Min_Int .. System.Max_Int.
   However, the base range of the new type is not inherited from
   root_integer, but is instead determined by the range or modulus
   specified by the integer_type_definition.  Integer literals are
   all of the type universal_integer, the universal type (see 3.4.1)
   for the class rooted at root_integer, allowing their use with the
   operations of any integer type.

It gives the formal background for returning the definition of
root_integer.  From the other side, returning the definition of the
user-defined type My_Int seems to be much more useful from an
application's viewpoint.

And the definition of Corresponding_Root_Type does not give the final
answer.

I think, that the clarification comments should be added to
Corresponding_Root_Type. My opinion is that this function should not
return definition of root integer types.

Another problem is that the ASIS says nothing about how the types of
Root_Type_Kinds may be obtained. I think some clarification comments
should be added.

------------------------------------------------------------------------------
-- Section 16.7  function Corresponding_Root_Type
------------------------------------------------------------------------------

    function Corresponding_Root_Type
                     (Type_Definition : in Asis.Type_Definition)
                      return Asis.Declaration;

------------------------------------------------------------------------------
--  Type_Definition - Specifies the derived_type_definition to query
--
-- This function recursively unwinds all type derivations and subtyping to
-- arrive at a full_type_declaration that is neither a derived type or a
-- subtype.
--
-- Appropriate Type_Kinds:
--      A_Derived_Type_Definition
--      A_Derived_Record_Extension_Definition
--
-- Returns Declaration_Kinds:
--      An_Ordinary_Type_Declaration
--      A_Task_Type_Declaration
--      A_Protected_Type_Declaration
--      A_Formal_Type_Declaration
--

!resolution  Accepted, with Modifications.
!date 97-03-25
!Notes

Two queries needed clarification with respect to implicit
root/universal types: Asis.Declarations.Names and
Asis.Definitions.Corresponding_Root_Type.

In Subclause 15.1, Asis.Declarations.Names, the following was added:

-- Returns Nil_Element_List for A_Declaration Elements representing the
-- (implicit) declarations of universal and root numeric type (that is,
-- if Type_Kind (Type_Declaration_View (Declaration)) = A_Root_Type_Definition.

In addition, the commentary for Subclause 16.7,
Asis.Definitions.Corresponding_Root_Type was changed as follows:

---------------------------------------------------------------------------------------
--  Type_Definition - Specifies the derived_type_definition to query
--
-- This function recursively unwinds all type derivations and subtyping to
-- arrive at a full_type_declaration that is neither a derived type nor a
-- subtype.
--
-- In case of numeric types, this function always returns some user-defined
-- type, not an implicitly defined root type corresponding to
-- A_Root_Type_Definition. The only ways to get implicitly declared numeric
-- root or universal types are to ask for the type of a universal expression
-- or from the parameter and result profile of a predefined operation working
-- with numeric types.

...

See also Issue #062.

Changes were made in ASIS version 2.0.M.