GOOPS functional setter

[Christopher Allan Webber]

I guess I never sent this to this list.  Here's a functional setter for
GOOPS classes.

Maybe nobody else would use it, but I've used it in a couple of projects
now, so figure I might as well share.

This is LGPLv3+.  Feel free to use.

==================================================

;; By Christopher Allan Webber, LGPLv3+; adapted from shallow-clone in GOOPS
(use-modules (oop goops))

(define-method (slot-fset (self <object>) slot-name value)
  "Return a new copy of SELF, with all slots preserved except SLOT-NAME
set to VALUE."
  (let* ((class (class-of self))
         (clone (allocate-instance class '())))
    (for-each (lambda (slot)
                (define slot-n
                  (slot-definition-name slot))
                (if (and (not (eq? slot-n slot-name)) (slot-bound? self slot-n))
                    (slot-set! clone slot-n (slot-ref self slot-n))))
              (class-slots class))
    ;; Set the particular slot we're overriding
    (slot-set! clone slot-name value)
    clone))

==================================================

(... Would anyone find this useful to include in Guile itself?  It might
also be nice to have a version that sets multiple fields at once, like
set-fields.  I'm not sure what the syntax should look like for that
though.  Maybe keep it simple?)

  (slot-multi-fset foo
    slot-name slot-val
    slot-name2 slot-val2)