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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)))
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