"mutate" now actually works

bin/pre.slime

@@ -5,6 +5,15 @@
     "Checks if the argument is nil."
     (= x nil)))
 
+(define append
+  (lambda (seq elem)
+    (if (nil? seq)
+        nil
+      (if (not (= (type (rest seq)) :pair))
+          ;; we are on the last element
+          (mutate seq (pair (first seq) elem))
+        (append (rest seq) elem)))))
+
 (define last
   (lambda (seq)
     "Returns the last element of the given sequence."
@@ -79,5 +88,5 @@ as compared to `reduce'."
            (print sep))
        ;; TODO(Felix): later we should use `extend' here:
        ;; (eval (extend (quote (printf :sep sep :end end)) (rest args)))
-       (eval (pair printf (pair :sep (pair sep (pair :end (pair end (rest args)))))))
+       (eval (extend '(printf :sep sep :end end) (rest args)))
        nil))))