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+; P08 Eliminate consecutive duplicates of list elements.
+; If a list contains repeated elements they should be replaced with a
+; single copy of the element. The order of the elements should not be changed.
+
+(def a (list "a" "a" "a" "a" "b" "c" "c" "a" "a" "d" "e" "e" "e" "e"))
+
+(func compress-iter (lst)
+    (def out (list))
+    (for-each lst
+        (if (or (empty? out) 
+                (not (eq? _item_ (last out))))
+            (redef out (append out _item_))))
+    out)
+
+; use the type system/dynamic dispatch
+(func compress-typ (lst)
+    (compress-typ lst (list)))
+
+; empty lists
+(func compress-typ (lst :nil acc)
+    acc)
+
+; non-empty lists, combined with a branch
+;(func compress-typ (lst :{:any} acc)
+;    (branch
+;        ((empty? acc) (compress-typ (rest lst) (list (first lst))))
+;        ((not (eq? (first lst) (last acc))) (compress-typ (rest lst) (append acc (first lst))))
+;        (#true (compress-typ (rest lst) acc))))
+
+; non-empty lists, non-empty accumulator
+(func compress-typ (lst :{:any} acc :{:any})
+    (if (eq? (first lst) (last acc)) 
+        (compress-typ (rest lst) acc)  ; don't append
+        (compress-typ (rest lst) (append acc (first lst)))))
+
+; non-empty lists, empty accumulator
+(func compress-typ (lst :{:any} acc :nil)
+    (compress-typ (rest lst) (list (first lst))))
+
+;(func extend (lst1 lst2)
+;    (reduce append lst2 lst1))
+
+; everything is an expression, so you could do this too
+; not sure if you'd want to, though, as you're creating
+; a list and then immediately killing it, which seems
+; like it's probably wasteful in the interpreter
+;(func compress-typ (lst :{:any} acc :{:any})
+;    (compress-typ (rest lst)
+;        (extend
+;            acc
+;            (if (not (eq? (first lst) (last acc)))
+;                (list (first lst))))))
+                
+
+(print (->string a))
+(print (->string (compress-iter a)))
+(print (->string (compress-typ a)))