Using clojure.contrib functions in slime REPL

Question

I want to use the functions in the clojure.contrib.trace namespace in slime at the REPL. How can I get slime to load them automatically? A related question, how can I add a specific namespace into a running repl?

On the clojure.contrib API it describes usage like this:

(ns my-namespace
  (:require clojure.contrib.trace))

But adding this to my code results in the file being unable to load with an "Unable to resolve symbol" error for any function from the trace namespace.

I use leiningen 'lein swank' to start the ServerSocket and the project.clj file looks like this

 (defproject test-project "0.1.0"
   :description "Connect 4 Agent written in Clojure"
   :dependencies [[org.clojure/clojure "1.2.0-master-SNAPSHOT"]
                  [org.clojure/clojure-contrib "1.2.0-SNAPSHOT"]]
   :dev-dependencies [[leiningen/lein-swank "1.2.0-SNAPSHOT"]
                      [swank-clojure "1.2.0"]])

Everything seems up to date, i.e. 'lein deps' doesn't produce any changes. So what's up?

Answer 1

1. You're getting "Unable to resolve symbol" exceptions because :require doesn't pull in any Vars from the given namespace, it only makes the namespace itself available.

   Thus if you (:require foo.bar) in your ns form, you have to write foo.bar/quux to access the Var quux from the namespace foo.bar. You can also use (:require [foo.bar :as fb]) to be able to shorten that to fb/quux. A final possiblity is to write (:use foo.bar) instead; that makes all the Vars from foo.bar available in your namespace. Note that it is generally considered bad style to :use external libraries; it's probably ok within a single project, though.

2. Re: automatically making stuff available at the REPL:

   The :require, :use and :refer clauses of ns forms have counterparts in the require, use and refer functions in clojure.core. There are also macros corresponding to :refer-clojure and :import.

   That means that in order to make clojure.contrib.trace available at the REPL you can do something like (require 'clojure.contrib.trace) or (require '[clojure.contrib.trace :as trace]). Note that because require is a function, you need to quote the library spec. (use and refer also take quoted lib specs; import and refer-clojure require no quoting.)

   The simplest way to have certain namespaces available every time you launch a Clojure REPL (including when you do it with SLIME) is to put the appropriate require calls in ~/.clojure/user.clj. See the Requiring all possible namespaces blog post by John Lawrence Aspden for a description of what you might put in user.clj to pull in all of contrib (something I don't do, personally, though I do have a (use 'clojure.contrib.repl-utils) in there).