Fix example a bit

README.org

@@ -6,16 +6,17 @@ the composition of more primitive operations.
 #+BEGIN_SRC lisp
   DATA-LENS> (funcall (on (compress-runs :collector 'combine-matching-lists)
                           (alexandria:compose 
-                           (over (juxt (element 0)
+                           (over (data-lens:juxt
+                                  (data-lens:element 0)
                                   'identity))
-                           (sorted 'string<)))
+                           (sorted 'char< :key (element 0))))
                       '("January" "February" "March" "April"
                         "May" "June" "July" "August"
                         "September" "October" "November" "December"))
   #| ==> ((#\A "April" "August")
           (#\D "December")
           (#\F "February")
-          (#\J "January" "July" "June")
+          (#\J "January" "June" "July")
           (#\M "March" "May")
           (#\N "November")
           (#\O "October")

lens.lisp

@@ -52,15 +52,18 @@
         acc
         (cons next acc))))
 
-(defun combine-matching-lists (&key (test 'eql) &allow-other-keys)
-  (lambda (acc next)
+(defun matching-list-reducer (test acc next)
   (if (and acc
            (funcall test (caar acc) (car next)))
       (cons (cons (caar acc)
                   (append (cdar acc)
                           (cdr next)))
             (cdr acc))
-        (cons next acc))))
+      (cons next acc)))
+
+(defun combine-matching-lists (&key (test 'eql) &allow-other-keys)
+  (lambda (acc next)
+    (matching-list-reducer test acc next)))
 
 (defun-ct compress-runs (&key (collector 'cons-new) (test 'eql) (key 'identity))
   (lambda (it)
@@ -72,7 +75,7 @@
 (defun-ct sorted (comparator &rest r &key key)
   (declare (ignore key))
   (lambda (it)
-    (apply #'sort (copy-seq it) comparator r)))
+    (apply #'stable-sort (copy-seq it) comparator r)))
 
 (defun-ct element (num)
   (lambda (it)