src/utilities.lisp, doc/misc.tex: Fix up `find-duplicates'.

  * Fix the inconsistent ordering behaviour which was the cause of a
    recent bug.  The implementation for lists is rather ugly, but it
    works without consing, which is a bonus.

  * Document the ordering behaviour.  And warn users away from non-
    hash-table-friendly `:test' functions more firmly, especially on
    lists.

diff --git a/doc/misc.tex b/doc/misc.tex
index 51767f6..ac89b6c 100644 (file)
--- a/doc/misc.tex
+++ b/doc/misc.tex
@@ -513,9 +513,14 @@ be implemented fairly easily using @|merge-lists| below.
   and $y$ are considered equal if and only if @|(funcall @<test> (funcall
   @<key> $x$) (funcall @<key> $y$))| returns non-nil.
 
+  The @<report> function is called as @|(funcall @<report> @<duplicate>
+  @<previous>)|.  Duplicates are reported in order; the @<previous> item is
+  always the first matching item in the sequence.
+
   This function will work for arbitrary @<test> functions, but it will run
-  much more efficiently if @<test> is @|eq|, @|eql|, @|equal|, or @|equalp|
-  (because it can use hash-tables).
+  much more efficiently if @<test> is @|eq|, @|eql|, @|equal|, or @|equalp|,
+  because it can use hash-tables.  (The generic implementation for lists is
+  especially inefficient.)
 \end{describe}
 
 

diff --git a/src/utilities.lisp b/src/utilities.lisp
index a496283..1670f55 100644 (file)
--- a/src/utilities.lisp
+++ b/src/utilities.lisp
@@ -717,18 +717,18 @@
                              (setf (gethash k seen) item)))))
                sequence)))
        ((listp sequence)
-        (mapl (lambda (tail)
-                (let* ((item (car tail))
-                       (rest (cdr tail))
-                       (match (member (funcall key item) rest
-                                      :test test :key key)))
-                  (when match (funcall report item (car match)))))
-              sequence))
+        (do ((tail sequence (cdr tail))
+             (i 0 (1+ i)))
+            ((endp tail))
+            (let* ((item (car tail))
+                   (match (find (funcall key item) sequence
+                                :test test :key key :end i)))
+              (when match (funcall report item match)))))
        ((vectorp sequence)
         (dotimes (i (length sequence))
           (let* ((item (aref sequence i))
                  (pos (position (funcall key item) sequence
-                                :key key :test test :start (1+ i))))
+                                :key key :test test :end i)))
             (when pos (funcall report item (aref sequence pos))))))
        (t
         (error 'type-error :datum sequence :expected-type 'sequence))))