Hi
On 25 August 2011 18:16, Shouxun Yang <[email protected]> wrote:
> Dear Clojurians,
>
> while playing with http://4clojure.com I found a perplexing behavior
> when I submit my own code for implementing my own poor implementation
> of my-flatten for problem 28:
>
> (defn my-flatten
> [coll]
> (loop [acc [] coll coll]
> (if-let [[a & coll] coll]
> (if (or (list? a) (vector? a))
> (recur acc (if (empty? coll)
> (vec a)
> (conj (vec a) coll)))
> (recur (conj acc a) coll))
> acc)))
>
> The above code failed the second test: ["a" ["b"] "c"].
>
> Instead of producing the correct result, it produces: ["a" "b" ("c")].
>
> But if I replace "(or (list? a) (vector? a))" with "(sequential? a)",
> the code works as expected.
>
> (defn my-flatten2
> [coll]
> (loop [acc [] coll coll]
> (if-let [[a & coll] coll]
> (if (sequential? a)
> (recur acc (if (empty? coll)
> (vec a)
> (conj (vec a) coll)))
> (recur (conj acc a) coll))
> acc)))
>
> While "(or (list? a) (vector? a))" will evaluates to true given a
> being '(c), somewhow in the above function it was evaluated to being
> false.
>
> Can anyone help me understand what is going on here?
Does this help?
user=> (class '("c"))
clojure.lang.PersistentList
user=> (if-let [[a & coll] coll] coll)
(["b"] "c")
user=> (class (if-let [[a & coll] coll] coll))
clojure.lang.PersistentVector$ChunkedSeq
user=> (list? (if-let [[a & coll] coll] coll))
false
user=> (vector? (if-let [[a & coll] coll] coll))
false
--
Michael Wood <[email protected]>
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