find out if a string with parens is balanced

balanced.cljs

#!/usr/local/bin/lumo
(ns balanced.core
  (:require [lumo.core :refer [*command-line-args*]]
            [clojure.string :refer [join]]))

(defn is-pair? [ch1 ch2] 
  (let [pairs {"(" ")"
               "[" "]"
               "{" "}"}]
    (= (get pairs ch1) ch2)))

(defn reduce-balanced [parens]
    (reduce (fn [stack ch]
              (if ((set "{[(") ch)
                (str stack ch)
                (if (is-pair? (last stack) ch)
                  (join (butlast stack))
                  "x"))) "" parens))

;----------- another implementation:

(defn remove-balanced [parens]
  (let [replaced (clojure.string/replace parens #"\(\)|\[\]|{}" "")]
    (if (= parens replaced)
      replaced
      (recur replaced))))

;----------- then call either one:

(defn balanced? [parens]
  (empty? (reduce-balanced parens)))

(def parens (first *command-line-args*))
(println (if (balanced? parens)
           "balanced"
           "not balanced"))

I like the approach using regex a lot! It resembles our initial idea where different 'stacks' of brackets are checked. 👍