is this a pure function?

[Nenad Perivojevic]

(ns qwerty.db
  (:require [clojure.java.jdbc :as j]))

(def mysql-db {:subprotocol "mysql"
               :subname "//127.0.0.1:3306/sakila"
               :user "root"
               :password "root"})

(defn get-actor-by-id [id]
  (first (j/query mysql-db
                  [(str "select * from actor where actor_id = " id)])))

I have one basic question, is function get-actor-by-id "pure" function?

[Tim Cooke]

From Wikipedia:

In computer programming, a function may be considered a pure function if both of the following statements about the function hold:

The function always evaluates the same result value given the same argument value(s). The function result value cannot depend on any hidden information or state that may change while program execution proceeds or between different executions of the program, nor can it depend on any external input from I/O devices

Evaluation of the result does not cause any semantically observable side effect or output, such as mutation of mutable objects or output to I/O devices

So, given those criteria would you say your function is 'pure'?

[Nenad Perivojevic]

I guess not, function result depends on database state in this case.
Thanks.

[Tim Cooke]

Exactly right. You're welcome.

[Sean Corfield]

And just a brief note about naming conventions: You'll see ! at the end of functions that specifically change their environment (like swap! and reset! for atoms) and in clojure.java.jdbc, you'll see ! at the end of functions that (potentially) modify the database (like insert! and delete!). However, just as deref does not have ! even though an atom's value may change each time you dereference it, so clojure.java.jdbc's query function also does not have ! even though the database could be changing and the results be different on each call.