Re: Am I missing something about (loop ... maximizing ...) ?

Raffael Cavallaro wrote:

Indeed. Here's rob Warnock's version with the full boat of loop
keywords using triplets instead of an association list:
 
CL-USER 22 > (defun find-maximizing-item (list &key (key #'identity)
(test #'<))
               (loop for item in list
                     for value = (funcall key item)
                     and position from 0
                     for current-triplet = (list item value position)
                     as max-triplet = current-triplet
                     then (if (funcall test (second max-triplet)
(second current-triplet))
                            current-triplet
                            max-triplet)
                     finally return
                     (values (first max-triplet) (second max-triplet)
(third max-triplet))))

Rejected by ABCL:

Debugger invoked on condition of type PROGRAM-ERROR:

Current LOOP context: "A compound form was expected, but ~S found.".


Rejected by SBCL:

; in: LAMBDA NIL
;     (LOOP FOR ITEM IN LIST
;           FOR VALUE = (FUNCALL KEY ITEM)
;           AND POSITION FROM ...)
;
; caught ERROR:
;   (in macroexpansion of (LOOP FOR ITEM ...))
;   (hint: For more precise location, try *BREAK-ON-SIGNALS*.)
;   A compound form was expected, but RETURN found.
;   current LOOP context: FINALLY RETURN (VALUES (FIRST MAX-TRIPLET)
;                                                (SECOND MAX-TRIPLET)
;                                                (THIRD MAX-TRIPLET)).

FIND-MAXIMIZING-ITEM
 
CL-USER 28 > (find-maximizing-item  (list "one" "two" "three" "fifteen"
"four" "five") :key #'length)
"fifteen"
7
3

It's somewhat shorter in Gauche Scheme.

(use gauche.collection)   ;; find-max

(define (find-maximizing-item items :optional (key identity))
  (find-max
    (map (lambda (x i) (list x (key x) i)) items (liota))
    :key cadr))


(find-maximizing-item  (list "one" "two" "three" "fifteen" "four"
  "five") string-length)
  ===>
("fifteen" 7 3)