Can getf use equal for comparison instead of eq? (common lisp)

Question

I am wondering if there a way that I can force getf to compare using equal instead of eq? I am using the ccl implementation of common lisp.

Answer 1

No. You have to use a different function; something approximately like this might do what you need:

(defun equal-getf (plist indicator)
  (second (member indicator plist :test #'equal)))

Edit

Here's a fixed version that treats the list properly as key/value pairs:

(defun equal-getf (plist indicator)
  (loop for key in plist by #'cddr
        for value in (rest plist) by #'cddr
        when (equal key indicator)
        return value))

Answer 2

I don't know if there's a way to "override" the default, see if you can find an impl using (describe 'getf) or (symbol-plist 'getf). A possible semplified implementation could be

(defun mgetf (l v)
  (if (< (length l) 2)
      NIL
    (if (equal (car l) v)
      (car (cdr l)) 
    (mgetf (nthcdr 2 l) v))))

EDITED : use nthcdr instead of double cdr.

Answer 3

This should do the job. It's not nicely recursive, but uses a straight-forward LOOP application. To allow it ti use an arbitrary equivalence predicate, the route to using an optional argument should be straight-forward.

(defun mgetf (place indicator)
  (loop for (key value . rest) on place by #'cddr
     if (equal key indicator)
     do (return value)))