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

Gauche Scheme:

Shorter by more than 100 characters.

(define (find-maximizing-item items :optional (key values))
(define (triple-it item i) (list item (key item) i))
(define (max-it item i triple)
(let ((candidate (triple-it item i)))
(if (or (not triple)
(> (cadr candidate) (cadr triple)))
candidate triple)))
(apply values
(fold
max-it
#f
items
(lrange 0))))

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

===>
"fifteen"
7 3