Running Our Application

Now that we have some familiarity with Clojure concepts and syntax, lets turn our attention back to the cider-tour application.

A Look at the Source

Keep the CIDER REPL buffer open and, in another buffer, open the core.clj file that resides under the src/cider-tour directory of the project.

core.clj is generated by Leiningen to provide boilerplate code for the application's entry-point (by convention the -main method).

The "out-of-the-box" version of core.clj generated by Leiningen looks like this: Screenshot - core.clj (original)

The contents were modified to look like this:

Screenshot - core.clj (modified)

core.clj contains three function calls:

• A ns function call to set the namespace to cider-tour.core for all functions/vars defined in the file. This is conceptually similar to the package statement in Java source files.

• A defn function call to define a function named say-hello. say-hello is a multi-arity function whose behavior (the "Hello" text printed) depends on the number of arguments passed to the function.

• A defn function call to define a function named -main that invokes the say-hello function with two arguments.

FYI

The -main and say-hello functions each have an embedded docstring that provides inline documentation on the usage of the function. The Clojure doc function displays parameter information and the docstring for a function (if defined).

Entering (doc -main) in the REPL returns the following:

Running the Code

Switch to your REPL window and type (-main) to execute the -main function:

Output

Executing (-main) invokes the say-hello with two arguments- "fellow Emacs user" and "Tellis (@tbellisiv)".

FYI

In the above screenshot the REPL displays the string nil after the "Hello" message. nil is the return value of the -main function. The REPL displays the return value of the function as well as any output sent to STDOUT. In Clojure the return value of a function is the value of the last evaluated expression in the function.

The last (only) evaluated expression in our -main function was println which always returns nil. Hence the return value of -main was nil (i.e. no value).

Tab Completion

Now, type (say- followed by the Tab key. CIDER will append the string hello to complete the say-hello symbol defined in our app. Type ) and then Enter to execute the say-hello function with no arguments:

Output