EIEIO and CL

[Chong Yidong <cyd@stupidchicken.com>]

Currently, the EIEIO library requires CL at runtime.  This is mainly due
to needing `deftype' and `typep' (EIEIO implements a subset of the CLOS
spec, which demand their existence).  If possible, it would be nice to
reduce this to a compile-time dependency, so that loading Semantic or
EDE does not load the CL library.

The `typep' requirement is solvable; the `deftype' requirement is the
more interesting.  Currently, eieio-defclass contains this code:

   ;; When using typep, (typep OBJ 'myclass) returns t for objects which
   ;; are subclasses of myclass.  For our predicates, however, it is
   ;; important for EIEIO to be backwards compatible, where
   ;; myobject-p, and myobject-child-p are different.
   ;; "cl" uses this technique to specify symbols with specific typep
   ;; test, so we can let typep have the CLOS documented behavior
   ;; while keeping our above predicate clean.
   (eval `(deftype ,cname ()
            '(satisfies
              ,(intern (concat (symbol-name cname) "-child-p")))))

The problem here is that the `cname' argument to the deftype CL macro
is, in general, determined at run-time.

Another possibility is to change eieio-defclass so that it defers this
deftype form till CL is loaded, by putting it on cl-macs-load-hook.
This assumes that the deftype is only useful if some later code calls
typep or typecase; if this assumption is wrong, that could lead to
subtle bugs.

Or, there may be a way to change `deftype' (or to provide a different CL
macro) that can do the right thing at compile-time.

Any suggestions?