Un-define expressions

As you are developing Clojure the names you use for functions and values can change. Rather than restart the REPL to remove these unwanted names you can un-define them.

Use the REPL command menu in the REPL buffer (Vim Insert or Emacs state) to undef a symbol:

, undef in the REPL buffer (Vim Insert / Emacs state) will prompt for a symbol to undefine.

TAB when typing the symbol name will popup a list of matching symbols available in the REPL. Select the name you wish to undef

Background

You can quickly remove a defined name from the REPL. This works for any def or defn expression that has been successfully evaluated in the REPL.

Removing a name from the expression helps you check if the code still works without that defined name. Also if any of the names are returning results from an older version of the name definition, you can ensure that the definition has been removed (potential showing incorrect dependencies elsewhere in your code).

When you evaluate a def or defn expression the name becomes part of the namespace available in the REPL.

So in the following example, when you evaluate the def expression for delete-me then you can call delete-me and get the string it points to as the return value.

Once you undefine the not-useful function in the REPL further calls to (not-useful) will cause an error.

(def delete-me "I should not be here, please remove me")

delete-me


(defn not-useful []
  (str "I really dont do anything worthwhile"))

(not-useful)

By un-evaluating the name delete-me from the REPL, the delete-me name is unbound from its value and no longer valid in the current namespace.