Compared to other languages, I've found Clojure makes it much easier to iteratively turn an idea into code. Say you're writing a pure function... You start wi

Compared to other languages, I've found Clojure makes it much easier to iteratively turn an idea into code. Say you're writing a pure function... You start with just data and a sense of how the output might look. Let's say I have APIs providing me with a user record and a list of transactions, and I want to get that person's balance... Maybe you start with some canned data (let [person {:name "Matt" :id 12345 :current_balance 100.10} txns [{:person_id 12345 :amt 10} {:person_id 44444 :amt 0.5} {:person_id 55555 :amt 10} {:person_id 12345 :amt 11} {:person_id 12345 :amt -5} {:person_id 66666 :amt 3}]] (->> txns count) ) => 6 and maybe you want to filter the transactions to just that user (let [person {:name "Matt" :id 12345 :current_balance 100.10} txns [{:person_id 12345 :amt 10} {:person_id 44444 :amt 0.5} {:person_id 55555 :amt 10} {:person_id 12345 :amt 11} {:person_id 12345 :amt -5} {:person_id 66666 :amt 3}]] (->> txns (filter #(= (:id person) (:person_id %))) count) ) => 3 then you want to extract the amount for each of those (let [person {:name "Matt" :id 12345 :current_balance 100.10} txns [{:person_id 12345 :amt 10} {:person_id 44444 :amt 0.5} {:person_id 55555 :amt 10} {:person_id 12345 :amt 11} {:person_id 12345 :amt -5} {:person_id 66666 :amt 3}]] (->> txns (filter #(= (:id person) (:person_id %))) (map :amt)) ) => (10 11 -5) and sum those amounts (let [person {:name "Matt" :id 12345 :current_balance 100.10} txns [{:person_id 12345 :amt 10} {:person_id 44444 :amt 0.5} {:person_id 55555 :amt 10} {:person_id 12345 :amt 11} {:person_id 12345 :amt -5} {:person_id 66666 :amt 3}]] (->> txns (filter #(= (:id person) (:person_id %))) (map :amt) (apply +)) ) => 16 and add that to the existing balance (let [person {:name "Matt" :id 12345 :current_balance 100.10} txns [{:person_id 12345 :amt 10} {:person_id 44444 :amt 0.5} {:person_id 55555 :amt 10} {:person_id 12345 :amt 11} {:person_id 12345 :amt -5} {:person_id 66666 :amt 3}] bal-change (->> txns (filter #(= (:id person) (:person_id %))) (map :amt) (apply +))] (+ bal-change (:current_balance person)) ) => 116.1 the function is done! (defn update-person-balance [{:keys [id current_balance]} txns] (let [bal-change (->> txns (filter #(= id (:person_id %))) (map :amt) (apply +))] (+ bal-change current_balance))) I posted here as a series of snippets, but this would have been a single block of code, refined and evaluated and refined and evaluated, over and over, in a REPL-integrated editor. It feels like sketching a portrait or sculpting clay. "But I can do that in any ol' REPL!" you might say. Try Clojure -- really try it, with an nREPL connected to your running application and to your editor, capturing inputs, playing them back, writing evaluation output as comments -- and then tell me you want to go back to your old REPL. A notebook environment is similar, though clumsier IMO. Come for the REPL-driven-development, stay for the immutability, the Java library ecosystem, the lisp syntax, the concurrency support, etc. I know going on and on about how great Clojure development is is basically a meme at this point, but that's because it's really great!