Hello World

Code

(ns hello-world.core)

(println "Hello world")
;; => nil

Explanation

Here’s a step-by-step explanation of the Clojure code snippet:

1. ns: The ns macro is used to define a namespace in Clojure. A namespace in Clojure (and in other programming languages) is a container that allows the developer to group related functions, macros, and data together. This aims to avoid naming conflicts between different parts of a program. The provided code snippet defines the namespace as hello-world.core.
2. hello-world.core: This is the name of the namespace declared. hello-world is usually the name of the project or application, and core is a conventional name for a main namespace in a Clojure application. However, these are just names and can be anything the programmer wishes.
3. println: The println function is a built-in function in Clojure for outputting text to the console. The text to be printed is passed as an argument to the println function.
4. "Hello world": This is a string argument passed to the println function. The println function will print the text “Hello world” to the console when the program is run.
5. ;; => nil: This is a comment in Clojure. Anything that follows ;; on the same line is a comment that the Clojure interpreter ignores. The => nil indicates the expected return value of the println function call. In Clojure, the println function returns nil after it prints to the console. It’s important to note that nil in Clojure is equivalent to null in other languages, which signifies no value or absence of value.
6. Clojure Syntax: Clojure uses a prefix notation which means that the function name comes before the arguments (e.g., (println "Hello world")). This is a characteristic of Lisp-like languages, which Clojure is part of. Code is organized in lists that are delimited by parentheses. The first element of a list is usually a function or macro to be invoked, followed by its arguments.
7. S-Expressions: Clojure, as a dialect of Lisp, follows the idea of “code as data” and uses s-expressions (symbolic expressions) to represent both code and data. An s-expression can be an atom or a list of s-expressions, as you see with the (println "Hello world").