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optimize seq (&) destructuring
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@richhickey
richhickey committed May 28, 2016
1 parent acd7c7a commit 0aa3467
Showing 1 changed file with 19 additions and 5 deletions.
24 changes: 19 additions & 5 deletions src/clj/clojure/core.clj
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Expand Up @@ -4255,28 +4255,42 @@
([& keyvals]
(clojure.lang.PersistentArrayMap/createAsIfByAssoc (to-array keyvals))))

;redefine let and loop with destructuring
;;redefine let and loop with destructuring
(defn destructure [bindings]
(let [bents (partition 2 bindings)
pb (fn pb [bvec b v]
(let [pvec
(fn [bvec b val]
(let [gvec (gensym "vec__")]
(loop [ret (-> bvec (conj gvec) (conj val))
(let [gvec (gensym "vec__")
gseq (gensym "seq__")
gfirst (gensym "first__")
has-rest (some #{'&} b)]
(loop [ret (let [ret (conj bvec gvec val)]
(if has-rest
(conj ret gseq (list `seq gvec))
ret))
n 0
bs b
seen-rest? false]
(if (seq bs)
(let [firstb (first bs)]
(cond
(= firstb '&) (recur (pb ret (second bs) (list `nthnext gvec n))
(= firstb '&) (recur (pb ret (second bs) gseq)
n
(nnext bs)
true)
(= firstb :as) (pb ret (second bs) gvec)
:else (if seen-rest?
(throw (new Exception "Unsupported binding form, only :as can follow & parameter"))
(recur (pb ret firstb (list `nth gvec n nil))
(recur (pb (if has-rest
(conj ret
gfirst `(first ~gseq)
gseq `(next ~gseq))
ret)
firstb
(if has-rest
gfirst
(list `nth gvec n nil)))
(inc n)
(next bs)
seen-rest?))))
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