@@ -225,9 +225,10 @@

 (defun transform-elt (elt fun)

   (lambda (it)

-    (append (subseq it 0 elt)

-            (list (funcall fun (nth elt it)))

-            (subseq it (1+ elt)))))

+    (concatenate (type-of it)

+                 (subseq it 0 elt)

+                 (list (funcall fun (elt it elt)))

+                 (subseq it (1+ elt)))))

 (defun key-transform (fun key-get key-set)

   (lambda (it)

@@ -259,3 +259,18 @@

   (5am:is (equalp #(1 2 3)

                   (funcall (data-lens:over '1+ :result-type 'vector)

                            #(0 1 2)))))

+

+(5am:def-test transform-elt (:suite :data-lens.lens :depends-on (and functionalize))

+  (5am:is (equal '(1 1 2)

+                 (funcall (data-lens:transform-elt 0 '1+)

+                          '(0 1 2))))

+  (5am:is (equal '(0 2 2)

+                 (funcall (data-lens:transform-elt 1 '1+)

+                          '(0 1 2))))

+  (5am:is (equalp #(0 1 3)

+                  (funcall (data-lens:transform-elt 2 '1+)

+                           (vector 0 1 2))))

+  (5am:is (equal "Abc"

+                 (funcall (data-lens:transform-elt 0 'char-upcase)

+                          "abc")))

+  )