difference in lein repl namespace for lein apps and libraries?

Question

I have no trouble calling functions in lein repl from my namespaces when I have created a lein new app .... But I don't seem to be able to call functions in lein repl when I just create a library project via lein new .... Details follow:

When I create a lein app with, say lein new app my-app, and then, from the project directory (the directory that contains project.clj), I do lein repl. The repl leaves me in the namespace my-app.core

my-app.core=>

I can now call functions in the repl, even functions defined in side files.

my-app.core=> (-main)
; Hello, world!
my-app.core=> (my-app.anotherfile/foo)
; Hey, there; this is foo from anotherfile

so long as I :require [my-app.anotherfile] in the ns macro of core.clj.

Ok, great; now I would like to do similarly with a lein library. So I lein new my-lib, then lein repl, and I'm in the user namespace:

user=>

huh? Ok, well, my lib contains a function that I want to call (this is just the one that leiningen creates by default)

(ns my-lib.core)

(defn foo
  "I don't do a whole lot."
  [x]
  (println x "Hello, World!"))

I try

user=> (in-ns 'my-lib.core)
my-lib.core=> (foo 42)
; CompilerException java.lang.RuntimeException: Unable to resolve symbol: foo in this context, compiling:(NO_SOURCE_PATH:1:1)

nope. How about this?

user=> (my-lib.core/foo 42)
; ClassNotFoundException two-files-lib.core  java.net.URLClassLoader$1.run (URLClassLoader.java:202

aha! Different error, but still no cure in sight. lein compile and lein javac don't seem to do anything either.

I have been unable to find or deduce the correct incantations in the docs or online and would be grateful for advice.

Michał Marczyk Michał Marczyk · Accepted Answer · 2013-04-14T16:27:47

In a default lein new project you need to require the namespaces you wish to use explicitly -- (require 'my-lib.core). in-ns simply creates a new empty namespace of the given name if it doesn't already exist, it doesn't load any code from the classpath.

App projects do this automatically and switch to the main namespace in the REPL task, because they have a :main foo.core entry in their project.clj by default. It's possible to do it for a library, but you shouldn't -- as a side effect, it causes AOT compilation of the main namespace, which is generally undesirable.

Instead, in lein2 you can use :repl-options {:init-ns my-lib.core}.

difference in lein repl namespace for lein apps and libraries?

1 Answers