A single issue here:
This
(defn bal-parens? [parens]
(let [replaced (clojure.string/replace parens "()" "")
checked (re-seq #"\(\)" replaced)]
(println checked)
(if-not (nil? checked) (bal-parens? replaced)
(do
(println (str "replaced is " replaced))
(empty? replaced)))))
is closer to what you'd expect (note I added "do" in the if-not clause).
An other flaw is using bal-parens? inside of bal-parens? which will
not get translated into tail-recursion.
Below you'll find a solution using loop-recur construct - the Clojure
way of providing tail-recursion.
(defn bal-parens? [parens]
(loop [str parens]
(if (= -1 (.indexOf str "()"))
(empty? str)
(let [replaced (clojure.string/replace str "()" "")]
(recur replaced)))))
Best,
Maciej
On 5 October 2014 00:02, <empty...@gmail.com> wrote:
> Hi,
>
> I am trying to write a function to return a boolean as to whether
> parenthesis are balanced or not?
>
> (defn bal-parens? [parens]
> (let [replaced (clojure.string/replace parens "()" "")
> checked (re-seq #"\(\)" replaced)]
> (println checked)
> (if-not (nil? checked) (bal-parens? replaced))
> (println (str "replaced is " replaced))
> (if (empty? replaced) true false)))
>
> (bal-parens? "(()())")
>
> I'd expect to see true here.
>
> But my output is:
>
> (())
> nil
> replaced is
> replaced is ()
> false
>
> I can't for the life of me think why, that when checked is nil and replaced
> is empty the function doesn't terminate!
>
> Many Thanks
>
> Aidy
>
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