X-Git-Url: https://git.distorted.org.uk/~mdw/sod/blobdiff_plain/3d1115c859f5f44f2ddb7f4b2fe8e7c43960f6b8..38b78e8763833fee8b41ecaf7586558e9b60d254:/src/utilities.lisp

diff --git a/src/utilities.lisp b/src/utilities.lisp
index b02fdf4..4935f8b 100644
--- a/src/utilities.lisp
+++ b/src/utilities.lisp
@@ -526,17 +526,21 @@
 			 (cdddr neigh-record) best-path)))))))
     dead))
 
-(export '(inconsistent-merge-error merge-error-candidates))
+(export '(inconsistent-merge-error
+	  merge-error-candidates merge-error-present-function))
 (define-condition inconsistent-merge-error (error)
   ((candidates :initarg :candidates
-	       :reader merge-error-candidates))
+	       :reader merge-error-candidates)
+   (present :initarg :present :initform #'identity
+	    :reader merge-error-present-function))
   (:documentation
    "Reports an inconsistency in the arguments passed to `merge-lists'.")
   (:report (lambda (condition stream)
 	     (format stream "Merge inconsistency: failed to decide between ~
 			     ~{~#[~;~A~;~A and ~A~:;~
 				  ~@{~A, ~#[~;and ~A~]~}~]~}"
-		     (merge-error-candidates condition)))))
+		     (mapcar (merge-error-present-function condition)
+			     (merge-error-candidates condition))))))
 
 (export 'merge-lists)
 (defun merge-lists (lists &key pick (test #'eql) (present #'identity))
@@ -593,7 +597,8 @@
 			      candidates))
 	   (winner (cond ((null leasts)
 			  (error 'inconsistent-merge-error
-				 :candidates (mapcar present candidates)))
+				 :candidates candidates
+				 :present present))
 			 ((null (cdr leasts))
 			  (car leasts))
 			 (pick