diff --git a/lens.lisp b/lens.lisp
index 066fd4f..5596a9b 100644
--- a/lens.lisp
+++ b/lens.lisp
@@ -179,6 +179,11 @@
   (lambda (seq)
     (map 'list selector seq)))
 
+(defun tap (cb)
+  (lambda (it)
+    (prog1 it
+      (funcall cb it))))
+
 (defun slice (start &optional end)
   (lambda (it)
     (subseq it start end)))
diff --git a/package.lisp b/package.lisp
index c639814..17fc338 100644
--- a/package.lisp
+++ b/package.lisp
@@ -21,7 +21,8 @@
            #:transform-elt #:denest #:op #:defalias #:<> #:<>1 #:== #:•
            #:∘ #:suffixp #:functionalize #:inc #:group-by #:keys
            #:conj #:disj #:delay #:of-type #:transform #:calling*
-           #:calling))
+           #:calling
+           #:tap))
 
 (defpackage :data-lens.transducers.internals
   (:use :cl)