Using an interactive shell (REPL)

Using an interactive shell (REPL)

How to:

Start with launching REPL:

user=> (println "Hello, REPL!")
Hello, REPL!

Define a function and try it out:

user=> (defn greet [name] (str "Hello, " name "!"))
user=> (greet "Clojure Programmer")
"Hello, Clojure Programmer!"

Experiment with data structures:

user=> (def my-map {:a 1 :b 2})
user=> (assoc my-map :c 3)
{:a 1, :b 2, :c 3}

Deep Dive

The REPL is key to the Lisp family’s interactive development philosophy, and Clojure, a modern Lisp dialect, makes great use of this tool. It dates back to the first Lisp REPL in the late 1950s. Alternatives in other languages include Python’s interpreter and Node.js’s console, but Clojure’s REPL has first-class status and is integral to the workflow.

A Clojure REPL session can be integrated into various environments like command-line, IDEs (such as IntelliJ with Cursive, or Emacs with CIDER), or browser-based tools like Nightcode. In a deeper sense, the REPL empowers the developer to manipulate the language’s constructs at run-time and carry states across various transformations, often leading to exploratory programming and more robust code.

The REPL’s functionality shines with tools like lein repl or clj, which allow for dependency management, various plugins, and project-specific customizations, leading to a more productive and flexible development process.

See Also