meta information about structure types

[Bruno H. <br...@cl...>]

Hi Sam,

Just proofreading the modifications of the last weeks. The access to
copier, boa constructor and predicate names is well done.

Thanks also for introducing the symbolic constants for
*defstruct-description-...-location*. I should have done this earlier.

Still I will make one change: instead of overloading the accessors
class-direct-slots, class-instance-size, I will separate these into
different functions structure-direct-slots, structure-instance-size,
structure-kconstructors, structure-copier etc. The reason is 1. that the
MOP API and your new API are neither a subset nor a superset - the
MOP covers all kinds of classes but not LIST/VECTOR structures, and
the structure API doesn't cover all kinds of metaclasses -, and
2. that the MOP API is based on a class object, whereas the structure API
is based on a symbol. Thus the structure API is better viewed as a layer
partially on top of the MOP API, in block diagram:

                            +--------------+
                            |   Structure  |
                            |      API     |
                    +--------------+       |
                    |      MOP     |       |
                    |      API     |       |
                    |              |       |
                    +--------------+-------+

Therefore it seems better to me to keep these APIs separate.
3. The user might be surprised if by calling
     (clos:class-direct-slots xyz),
where xyz does not name a class, he gets a result not related to classes.

Bruno