lein:tldr:61c04

The command "lein repl" is used to start a REPL (Read-Eval-Print Loop) session for a Clojure project that is managed by Leiningen.

Leiningen (often abbreviated as "lein") is a build and dependency management tool for Clojure projects. It provides various commands to automate project tasks, including managing dependencies, compiling code, running tests, and starting a REPL.

A REPL is an interactive programming environment where you can enter expressions, evaluate them immediately, and see the results. It allows you to experiment with code, test functions, and interactively develop your application.

When you run the command "lein repl" in a Clojure project directory, Leiningen starts a REPL session by launching the Clojure runtime environment. It loads the project dependencies and provides you with a prompt where you can enter Clojure expressions to be evaluated.

Once the REPL is running, you can enter any valid Clojure expression, and it will be read, evaluated, and the result will be printed for you to see. You can also define functions, manipulate data structures, and interact with your project code while the REPL is active.

Using a REPL is beneficial for exploring and experimenting with Clojure code, debugging, and testing. It provides an iterative and interactive development experience, where you can quickly evaluate code and see immediate results, making it easier to understand and refine your code.