From Newsgroup: comp.lang.lisp

John Thingstad wrote:

It is the trivial to check for duplicates and lookup key

(defun duplicate-value-check ()
(let* ((values (loop for v in (cdr *enum*) by #'cddr collect v))
(sorted-values (sort values #'<))
(position (mismatch sorted-values
(remove-duplicates sorted-values))))
(when position
(let ((index (nth position sorted-values)))
(error "key ~A has a value ~D duplicated"
(nth (* index 2) *enum*) (nth index sorted-values))))))

Testing with ABCL:

(setq *enum* '(a 2 b 3 c 4 d 5 e 6 f 7 g 8 h 9 i 2))
(duplicate-value-check)

CL-USER(3): Debugger invoked on condition of type SIMPLE-ERROR:
key C has a value 3 duplicated

It should have been:
key i has a value 2 duplicated

Gauche Scheme

(define (dup-check plist)
(let1 seen '()
(do-plist ((k v) plist)
(if (member v seen)
(errorf "Key ~a has dup. value ~a." k v)
(push! seen v)))))

(dup-check '(a 2 b 3 c 4 d 3 e 6 f 7 g 8 h 3 i 42))

*** ERROR: Key d has dup. value 3.
--
[T]he problem is that lispniks are as cultish as any other devout group and basically fall down frothing at the mouth if they see [heterodoxy].
--- Kenny Tilton
The good news is, it's not Lisp that sucks, but Common Lisp. --- Paul Graham --- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: comp.lang.lisp

"B. Pym" <Nobody447095@here-nor-there.org> writes:

Testing with ABCL:

(setq *enum* '(a 2 b 3 c 4 d 5 e 6 f 7 g 8 h 9 i 2))
(duplicate-value-check)

CL-USER(3): Debugger invoked on condition of type SIMPLE-ERROR:
key C has a value 3 duplicated

It should have been:
key i has a value 2 duplicated

Gauche Scheme

(define (dup-check plist)
(let1 seen '()
(do-plist ((k v) plist)
(if (member v seen)
(errorf "Key ~a has dup. value ~a." k v)
(push! seen v)))))

(dup-check '(a 2 b 3 c 4 d 3 e 6 f 7 g 8 h 3 i 42))

*** ERROR: Key d has dup. value 3.

Because Common LisprCOs rCylooprCO macro supports iterating over
the CDRs of lists and destructuring, the CL version of
rCydup-checkrCO is similar:

(defvar *enum* '(a 2 b 3 c 4 d 5 e 6 f 7 g 8 h 9 i 2))

(defun dup-check (plist)
"Verify that property list PLIST has no duplicate values. An error
is issued if any are found."
(loop
for (k v) on plist by #'cddr
if (member v unique) do
(error "key ~A has a value ~D duplicated" k v)
else
collect v into unique
finally (return 'no-duplicates)))

(dup-check *enum*)

Run-time error: "key I has a value 2 duplicated"

(dup-check '(a 2 b 3 c 4 d 3 e 6 f 7 g 8 h 3 i 42))

Run-time error: "key D has a value 3 duplicated"

(dup-check
'(a 2 b 3 c 4 d 5 e 6 f 7 g 8 h 9))

NO-DUPLICATES

See "The for-as-on-list subclause": http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/HyperSpec/Body/sec_6-1-2-1-3.html
--
The lyf so short, the craft so long to lerne.
- Geoffrey Chaucer, The Parliament of Birds.
--- Synchronet 3.21a-Linux NewsLink 1.2