On Tue, Dec 10, 2013 at 6:29 PM, Vincent Chen <noodle...@gmail.com> wrote:
> Try this (not tested, might be missing parens and whatnot):
>
> (defn slice [x s n]
> (loop [[h & tail] x, s s, n n, acc []]
> (cond
> (zero? n) acc
> (zero? s) (recur tail s (dec n) (conj acc h))
> :else (recur tail (dec s) n acc))))
>
> Few notes:
> - When trying for tail recursions, use an accumulator. The accumulator
> carries the eventual result, which is returned at the base case.
> - Since we're destructuring into head and tail, I used vectors. conj
> will push to the end of the vector.
> - In Clojure, vectors tend to be more natural than lists. Accumulating
> into lists usually requires a reverse in the base case.
If you're going to go with vectors, why not go transient as well?
(defn slice [x s n]
(loop [[h & tail] x, s s, n n, acc (transient [])]
(cond
(zero? n) (persistent! acc)
(zero? s) (recur tail s (dec n) (conj! acc h))
:else (recur tail (dec s) n acc))))
Might be more runtime efficient.
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