diff --git a/tk/listlogic.scm b/tk/listlogic.scm
index 8fdd602..0f2fce8 100644
--- a/tk/listlogic.scm
+++ b/tk/listlogic.scm
@@ -1,7 +1,7 @@
 (define-module (tk listlogic)
-  #:export ('flatten
-            'lp&
-            'l&
+  #:export (flatten
+            lp&
+            l&
             )
   #:duplicates (warn-override-core warn ))
 
diff --git a/tk/ports.scm b/tk/ports.scm
new file mode 100644
index 0000000..a6e82ee
--- /dev/null
+++ b/tk/ports.scm
@@ -0,0 +1,7 @@
+(define-module (tk ports)
+  #:export (port-rewind!)
+  )
+
+(define (port-rewind! port chars n)
+  (receive (rw rest) (split-at! chars n)
+    (for-each (lambda (c) (unget-char port c)) rw) rest))