OOP: implementing multiple inheritance.

Multiple inheritance is too useful to ignore any longer.

* lib.c (subtypep): Perform subtypep calculation between two
struct types via the new struct_subtype_p function.
It's too complicated now to do with ad hoc code outside of
struct.c.

* share/txr/stdlib/struct.tl (defstruct): This macro now needs
to deal with the super argument being possibly a list of base
types instead of a single one.

* strut.c (struct struct_type): Member super and super_handle
are removed. New member nsupers, supers, and sus.
(struct_init): The super function re-registered; it has an
optional argument.
(call_stinitfun_chain): The compat code here must now access
the supertype differently. We don't bother dealing with
multiple inheritance in the compat case; programs requesting
compatibility with TXR 151 shoudn't be trying to use multiple
inheritance.
(get_struct_handles, count_super_stslots, get_super_slots,
find_super_for_slot): New static functions, to off-load some
new complexity from make_struct_type.
(make_struct_type): Handle the increased complexity due to
multiple inheritance.
(super): Takes an additional argument now, to request which
supertype to retrieve. Defaults to zero: the first one.
(struct_type_destroy): Free the sus array.
(struct_type_mark): Mark the supers slot.
(call_initfun_chain): Call init functions of all bases, in
right-to-left order.
(call_postinitfun_chain): Likewise for postinit functions.
(call_super_method, call_super_fun, super_method): Use the
first base as the supertype.  This requirement feels bad; it
needs to be revisited.
(do_struct_subtype_p): New static function.
(struct_subtype_p): New function.
(ancestor_with_static_slot): New static function.
(method_name): Revised for multiple inheritance; now relies on
ancestor_with_static_slot to find the original ancestor that
has brought in a method, so we can use that type in the
method name.

* struct.h (super): Declaration updated.
(struct_subtype_p): Declared.

* tests/012/oop-mi.expected: New file.

* tests/012/oop-mi.tl: New test cases.

* txr.1: Revised in order to document multiple inheritance.

1 files changed, 2 insertions, 1 deletions

diff --git a/struct.h b/struct.h
index 1850814e..78701270 100644
--- a/struct.h
+++ b/struct.h
@@ -47,7 +47,7 @@ val struct_get_initfun(val type);
 val struct_set_initfun(val type, val fun);
 val struct_get_postinitfun(val type);
 val struct_set_postinitfun(val type, val fun);
-val super(val type);
+val super(val type, val idx);
 val make_struct(val type, val plist, struct args *);
 val struct_from_plist(val type, struct args *plist);
 val struct_from_args(val type, struct args *boa);
@@ -75,6 +75,7 @@ val slots(val stype);
 val structp(val obj);
 val struct_type(val strct);
 val struct_type_name(val stype);
+val struct_subtype_p(val sub, val sup);
 val method(val strct, val slotsym);
 val method_args(val strct, val slotsym, struct args *);
 val super_method(val strct, val slotsym);