Hot-load libraries in Projects¶
From Clojure 0.12 onward, libraries can be hot-loaded into the running REPL using clojure.repl.deps functions.
Use a rich comment block when using source code files to evaluate code in the REPL, i.e. a REPL connected editor.
Update and synchronise the project deps.edn configuration when there is certainty that a library should become part of the project.
Reload Namespaces using Practicalli Reloaded REPL workflow
Practicalli REPL Reloaded workflow provides additional tools to reload namespaces in a running REPL process, without loosing the current REPL state.
Rich Comment Block¶
A rich comment block separates hot-load code to ensure is only evaluated manually and not included when evaluating the whole namespace.
Adding a single library
Clojure LSP snippets for hot-loading
rich-comment-hotload snippet from Practicalli Clojure LSP Config expands to a rich comment block with a require for clojure.repl.deps, with an add-lib.
deps-maven and deps-git snippets ensure the correct syntax is used for thecoord argument of add-lib and add-libs functions for a library.
Hot-load Web Server¶
Create a web server from scratch, serving pages generated from hiccup.
All libraries are hot-loaded as the code is written, showing its possible to write a application when only starting the REPL once.
REPL log for hot-load web server
(comment
;; run REPL with :lib/hotload alias
(require '[clojure.repl.deps :refer [add-lib]])
;; add latest http-kit library
(add-lib 'http-kit/http-kit {:mvn/version "2.5.1"}})
;; => (http-kit/http-kit)
;; Require the namespace from the http-kit library
(require '[org.httpkit.server :as app-server])
;; Define a handler for http requests
(defn welcome-page
[request]
{:status 200
:body "Welcome to the world of Clojure CLI hotloading"
:headers {}})
;; Start the application server with the handler
(app-server/run-server #'welcome-page {:port (or (System/getenv "PORT") 8888)})
;; Visit http://localhost:8888/ to see the welcome-page
;; Hotload Hiccup to generate html for the welcome page
(add-lib 'hiccup/hiccup {:mvn/version "2.0.0-RC1"})
(require '[hiccup.core :as hiccup])
(require '[hiccup.page :as hiccup-page])
;; Create a page template
(defn page-template [content]
(hiccup-page/html5
{:lang "en"}
[:head (hiccup-page/include-css "https://cdn.jsdelivr.net/npm/bulma@0.9.0/css/bulma.min.css")]
[:body
[:section {:class "hero is-info"}
[:div {:class "hero-body"}
[:div {:class "container"}
[:h1 {:class "title"} (:title content) ]
[:p {:class "subtitle"} (:sub-title content)]]]]]))
;; Check the page template returns HTML
(page-template {:title "Hotload Libraries in the REPL"
:sub-title "REPL driven development enables experimentation with designs"})
;; redefine the welcome page to call the page template
(defn welcome-page
[request]
{:status 200
:body (page-template {:title "Hotload Libraries in the REPL"
:sub-title "REPL driven development enables experimentation with designs"})
:headers {}})
;; Visit http://localhost:8888/ and refresh the page to see the new welcome-page
)
Synchronising Library Dependencies¶
sync-deps function will ensure all libraries defined in the :deps key of the project deps.edn configuration are loaded in the currently running REPL.
If new libraries have be added to the :deps key they will be downloaded and included (added to the JVM class path).
This approach ensures added libraries become part of the normal project dependency configuration.
Comment Reader Macro for optional libraries
The #_ comment reader macro ignores the next form. A #_#_ will ignore a library and coord of a dependency without breaking the syntax of the deps.edn configuration.
To hotload a commented library, remove #_#_ and run sync-deps.