如何在deps.edn中设置*print-length*默认值（替代Leiningen的project.clj）

Great question! Unlike Leiningen's project.clj which had straightforward profile-based options for setting dynamic vars like *print-length*, deps.edn requires a bit more explicit setup—but there are several clean, reliable approaches to get this working. Here are the most common methods:

1. Use a user.clj namespace (simplest approach) #

Clojure automatically loads a user namespace from your classpath when starting a REPL, making this the easiest way to set default values for dynamic vars.

• Create a src/user.clj file (or add to an existing one) with:

  (ns user)
  ;; Set your desired default print length
  (set! *print-length* 10)
  

• Since src/ is included in the default classpath for deps.edn projects, just start your REPL with clj—the user namespace will load automatically, and *print-length* will be set to your chosen value.

2. Inject initialization code via JVM options #

You can pass a Clojure expression directly to the JVM to execute on startup using the clojure.main.init system property. This works well if you want to tie the setting to a specific alias.

Add this to your deps.edn:

{:aliases
 {:dev {:jvm-opts ["-Dclojure.main.init='(set! *print-length* 10)'"]}}}

Then start your REPL with:

clj -A:dev

Note: If you're using Windows Command Prompt, you may need to adjust the quoting (e.g., use double quotes around the entire JVM option and escape inner quotes).

3. Load a dedicated initialization namespace #

If you prefer to keep your setup organized in a separate namespace (instead of user.clj), you can create an init namespace and load it on startup.

• First, create src/dev/init.clj:

  (ns dev.init)
  (set! *print-length* 10)
  ;; Add other dev-specific settings here if needed
  

• Update your deps.edn to include the src/dev path and load the namespace on startup:

  {:aliases
   {:dev {:extra-paths ["src/dev"]
          :main-opts ["-e" "(do (require 'dev.init) (clojure.main/repl))"]}}}
  

• Start your REPL with clj -A:dev—this will load the dev.init namespace (setting *print-length*) and then launch the REPL.

All of these methods will ensure *print-length* is set to your preferred default every time you start your Clojure REPL via deps.edn. The user.clj approach is generally the most low-friction for most projects!

内容的提问来源于stack exchange，提问作者Mert Nuhoglu