Web Development with Clojure, 2nd Edition

The Read-Evaluate-Print Loop

Another big aspect of working in Clojure is the read-evaluate-print loop (REPL). In many languages you write the code, and then you run the entire program to see what it does. In Clojure, most development is done interactively using the REPL. In this mode we can see each piece of code we write in action as soon as it’s written.

In nontrivial applications it’s often necessary to build up a particular state before you can add more functionality. For example, a user has to log in and query some data from the database, and then you need to write functions to format and display this data. With a REPL you can get the application to the state where the data is loaded and then write the display logic interactively without ...