diff --git a/data-lens-fset.lisp b/data-lens-fset.lisp
index fc4f872..c953f37 100644
--- a/data-lens-fset.lisp
+++ b/data-lens-fset.lisp
@@ -17,9 +17,9 @@
   (data-lens.transducers:transducer-lambda
     ((acc next)
      (fset:with acc next))))
-(defmethod data-lens:functionalize ((it fset:set))
-  (lambda (key)
-    (nth-value 1 (fset:lookup it key))))
+(defmethod data-lens:functionalize ((set fset:set))
+  (lambda (it)
+    (fset:contains? set it)))
 (defmethod data-lens:extract-key ((it fset:set) key)
   (nth-value 1 (fset:lookup it key)))
 (defun make-set-lens (item)
@@ -114,3 +114,4 @@
   (funcall (funcall (make-set-lens loc)
                     cb)
            rec))
+
diff --git a/optics.lisp b/optics.lisp
index 0367eaf..10bfe9a 100644
--- a/optics.lisp
+++ b/optics.lisp
@@ -210,8 +210,8 @@ contain the new value at the location focused by the lens."
   (defun a-lens (cb)
     (lambda (foo)
       (fw.lu:prog1-bind (new (clone foo))
-                        (setf (a new)
-                              (funcall cb (a foo))))))
+        (setf (a new)
+              (funcall cb (a foo))))))
   (view 'a-lens
         (over 'a-lens '1+
               (set 'a-lens 2
@@ -222,10 +222,14 @@ contain the new value at the location focused by the lens."
   (:method ((rec hash-table) cb loc)
     (funcall (funcall (make-hash-table-lens loc)
                       cb)
+             rec))
+ (:method ((rec vector) cb loc)
+    (funcall (funcall (make-list-lens loc)
+                      cb)
              rec)))
 
 (defun lens (loc)
-  "A lens for updating a hash-table, discarding previous values"
+  "extensible lens using a multimethod for internal implementation"
   (lambda (cb)
     (lambda (rec)
       (generic-lens rec cb loc))))
diff --git a/transducer-protocol.lisp b/transducer-protocol.lisp
index 6035a25..d615436 100644
--- a/transducer-protocol.lisp
+++ b/transducer-protocol.lisp
@@ -56,8 +56,10 @@
 
 CONSTRAINT: SEQ should be copied, not modified"))
 
+(declaim (inline exit-early))
 (defun exit-early (acc)
   (throw 'done acc))
+(declaim (notinline exit-early))
 
 (defun transduce (xf build seq)
   (let* ((xf (etypecase xf