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+; P09 Pack consecutive duplicates of list elements into sublists.
+; If a list contains repeated elements they should be placed in separate sublists.
+
+(def a (list "a" "a" "a" "a" "b" "c" "c" "a" "a" "d" "e" "e" "e" "e"))
+
+; the list, the most recent value, the accumulator
+(func pack-dup (lst)
+    (pack-dup lst "" (list)))
+
+(func pack-dup (lst prev acc)
+    (branch
+        ((empty? lst) acc) ; if we're done, return acc
+        ((eq? (first lst) prev) ; the item is the same as the previous item
+            (pack-dup 
+                (rest lst) 
+                prev 
+                (append  ; add item to the last list in acc
+                    (most acc) 
+                    (append 
+                        (last acc) 
+                        prev))))
+        (#true
+            (pack-dup 
+                (rest lst) 
+                (first lst) 
+                (append 
+                    acc 
+                    (list (first lst)))))))  ; add new list with this item
+
+(print (->string a))
+(print (->string (pack-dup a)))