-(defun find-if (predicate sequence &key (key #'identity))
- (do-sequence (x sequence)
- (when (funcall predicate (funcall key x))
- (return x))))
+(defun position (elt sequence
+ &key key (test #'eql testp)
+ (test-not #'eql test-not-p)
+ (start 0) end)
+ ;; TODO: Implement START and END efficiently for all the sequence
+ ;; functions.
+ (let ((end (or end (length sequence))))
+ (do-sequence (x sequence index)
+ (when (and (<= start index)
+ (< index end)
+ (satisfies-test-p elt x
+ :key key :test test :testp testp
+ :test-not test-not :test-not-p test-not-p))
+ (return index)))))