Oracle SQL. Error creating type I'm learning SQL.

When I try to create a type in Oracle SQL:

CREATE TYPE boolean_typ AS OBJECT
(valor char(5) CHECK (VALUE IN ('true', 'false', NULL)) );
/


I get this error:

Warning: Type created with compilation errors.


It gives no explanation on what is the error. May you help me?
Type the following command right after you receive your error-message:

show errors


Show here:

SQL&gt; CREATE TYPE boolean_typ AS OBJECT
  2  (valor char(5) CHECK (VALUE IN ('true', 'false', NULL)) );
  3  /

Warning: Type created with compilation errors.

SQL&gt; show errors
Errors for TYPE BOOLEAN_TYP:

LINE/COL ERROR
-------- -----------------------------------------------------------------
2/16     PLS-00103: Encountered the symbol "CHECK" when expecting one of
         the following:
         := ) , not null default external character

SQL&gt; drop type boolean_typ;

Type dropped.

SQL&gt; exit