Using libraries in the REPL¶

A library should be defined as a dependency in order to call its functions from within the REPL.

In the deps.edn file, the :deps key defines libraries that are always part of the project.

Optional libraries are defined via :aliases, only included when the alias is used in the command to to start the REPL, e.g. clojure -M:alias/name

From Clojure 0.12 libraries can be hot-loaded into a REPL without restarting it.

{:paths ["src" "resources"]

 :deps
 {org.clojure/clojure {:mvn/version "1.10.3"}}

 :aliases
 {
  :database/h2
  {:extra-deps {com.h2database/h2                 {:mvn/version "2.1.210"}
                com.github.seancorfield/next.jdbc {:mvn/version "1.2.772"}}}
 #_()}

Include library¶

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

Start the REPL including the :database/h2 alias to include every library defined in the :deps key and libraries in the :database/h2 alias. This example is using rebel readline rich terminal UI

clojure -M:repl/rebel

This command will include

Add aliases to include optional libraries, such as those used for development. In this example, the H2 database and next.jdbc libraries are included along with those libraries in the :deps key of deps.edn

clojure -M:database/h2:repl/rebel

Load namespace¶

At the REPL prompt, require a namespace from the project to load all the code from that namespace and any namespaces required.

If a project was created with the command clojure -T:project/new :template app :name practicalli/status-monitor then the main namespace will be practicalli.status-monitor

(require '[practicalli.status-monitor])

The require function loads all the code from the main namespace. When an ns form is read, required namespaces in the ns form are also loaded.

Reload namespace¶

Clojure is a dynamic environment, so changes to function definitions (defn) and shared symbol names (def) can be updated without restarting the REPL.

require loads the code from the specified namespace. Using the :reload option forces the namespace to be loaded again, even if it was already loaded.

When changes are made to a namespace in the source code file, :reload ensures those changes become the code running in the REPL

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

If errors occur when loading or reloading 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] :reload :verbose)

Hot-load library¶

From Clojure 0.12 onward, libraries can be added to a running REPL session without having to restart it.

Require the clojure.repl.deps library and refer the add-lib and add-libs functions.

(require '[clojure.repl.deps.:refer [add-lib add-libs]])

Hot-load a library into the REPL using the fully qualified name of the library. If a version (coord) is not provided, the latest release of that library will be used.

(add-lib 'domain/library {:mvn/version "release-version"}})

Multiple libraries can be hot-loaded in a single add-libs expression

(add-libs '{hhgttg/meaning {:mvn/version "4.2.0"}
            eternity/room  {:mvn/version "1.0.1"}})

Hot-load hiccup in a terminal REPL¶

The hiccup library converts Clojure structures into html, where a keyword in a vector represent an html tag, optionally with CSS classes for styling.

Require the Clojure REPL library

(require '[clojure.repl.deps :refer [add-lib]])

Load the hiccup library using the add-lib function, specifying a specific release version.

(add-lib 'hiccup/hiccup {:mvn/version "2.0.0-RC1"})

Require the hiccup library so its functions are accessible from the current namespace in the REPL.

(require '[hiccup.core :as hiccup])

Enter an expression using the hiccup/html function to convert a clojure data structure to html.

(hiccup/html [:div {:class "right-aligned"}])

The hiccup expression returns a string of the html code.