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

[Denis Bueno]

Define it like so, as a struct:

(defstruct (vec2 (:type vector))
  a
  b)

Then you can do:

 > (make-vec2 :a 'a-val :b 'b-val)
#(A-VAL B-VAL)
 > (vec2-a *)
A-VAL
 > (vec2-b **)
B-VAL

On 01 Mar 2005, at 02.14, Andrew P. Lentvorski, Jr. wrote:

> 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
>
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>
--
Denis Bueno
PGP: http://pgp.mit.edu:11371/pks/lookup?search=0xA1B51B4B&op=index
"To be positive: To be mistaken at the top of one's voice." - Ambrose 
Bierce