Using Clojure libraries and projects in the REPL

A Clojure library or project can be used in the REPL, by requiring the main namespace

Run the REPL in the root of the project with a deps.edn file

A library needs to be included as a dependency in order to use it in the REPL.

Using an alias

clojure -A:database/next.jdbc:database/h2

Alternatively, specify the library names on the command line using the --deps argument

Or add the library as a dependency to a project and run the REPL from the root of that project.

Start the REPL and load the project

Open a terminal and change to the root of the Clojure project directory, where the deps.edn file can be found.

Start the REPL (in this example using rebel readline)

clojure -M:repl/rebel

At the REPL prompt, require the main namespace of the project.

If the project was created with the command clojure -M:new app practicalli.status-monitor-service, then the main namespace will be practicalli.status-monitor-service

(require '[practicalli.status-monitor-service])

The require function loads all the vars (def, defn, etc) definitions from the main namespace. The ns form is also read and any required namespaces that are in the ns form are loaded.

Reloading the namespace

When changes are made to a namespace in the source code file, those changes can be loaded into the repl by reloading the namespace the change was made in.

(:require '[fully.qualified.namespace] :reload)

Hot-load libraries

add-libs function from the library is an unofficial approach to hot-loading library dependencies without having to restart the REPL or add those dependencies to the project deps.edn. This provides a simple way to try out libraries.

See hotload of libraries for details.


If errors occur when loading the namespace with require, the :verbose option will show all the namespaces that are loaded. This may show issues or help track down conflicting namespaces or functions.

(require '[practicalli.status-monitor-service] :verbose)

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