[Openmcl-devel] Applying sequence functions to a new type

[Andrew P. Lentvorski, Jr.]

This is probably a really stupid question, but how do I define the 
sequence functions so that they apply to a new class?

For example, let's say I want a stupid class that always has two 
elements a and b.  I would like to be able to access a and b as thought 
they were elements 0 and 1 of a sequence.

Welcome to OpenMCL Version (Beta: Darwin) 0.14.2-040925!
? (defclass Vec2 ()
            ((a :accessor a
                :initarg :a)
             (b :accessor b
                :initarg :b)))
#<STANDARD-CLASS VEC2>
? (setq v2 (make-instance 'Vec2 :a 7 :b 11))
#<VEC2 #x644EAB6>
? (elt v2 0)
 > Error in process listener(1): value #<VEC2 #x644EAB6> is not of the 
expected type SEQUENCE.
 > While executing: CCL::SEQUENCE-TYPE
 > Type :POP to abort.
Type :? for other options.
1 > ^D
? ;; Okay, let's try a different tack
(defclass Vec2 (sequence)
            ((a :accessor a
                :initarg :a)
             (b :accessor b
                :initarg :b)))
 > Error in process listener(1): The class #<BUILT-IN-CLASS SEQUENCE> 
was specified as a
 >                               super-class of the class 
#<STANDARD-CLASS VEC2>;
 >                               but the meta-classes #<STANDARD-CLASS 
BUILT-IN-CLASS> and
 >                               #<STANDARD-CLASS STANDARD-CLASS> are 
incompatible.
 > While executing: #<CCL::STANDARD-KERNEL-METHOD SHARED-INITIALIZE 
:AFTER (CCL::SLOTS-CLASS T)>
 > Type :POP to abort.
Type :? for other options.
1 >
? ;; Okay, that sure didn't work

So how do I define a function elt or redefine Vec2 such that elt can be 
written to work with it?

Thanks,
-a