Clojure Course - Introduction

Clojure Course

Part 1 - Introduction

Clojure is a modern, mature, functional programming language, created by Rich Hickey in 2007.

Main features:

Clojure is a dialect of LISP (List Processor). This language family was first introduced by John McCarthy in 1958, and it has several notable variants, including Common Lisp, Scheme, Racket and Emacs Lisp. Clojure is one of the more recent members of the family.
Lisp syntax is characterized (and often mocked) by extensive use of parenthesis. Lisp programmers consider this a gift, rather than an annoyance - you'll learn how to embrace it too :)
Clojure has a powerful macro system, which provides insane extensibility to the language.
The Lisp philosophy that treats code as data, grants Clojure the ability to change programs at runtime, and supports live coding. The REPL (read-eval-print loop) as an interactive development tool, is an important component of the Clojure programming experience.
Clojure commands a full arsenal of FP features, such as immutability, function composition, lazy evaluation and a preference for pure functions. Tons of useful tools are already implemented in the standard library.
Dynamic - this applies not only to the type system (as opposed to static typing), but also to dynamic polymorphism, flexible heterogenous collections, and the explicit aim to make developers more productive.
Clojure's built-in data types and collections are versatile, fast and efficient.
Great support for concurrency.
Clojure is a compiled, hosted language. It was designed to take advantage of the platform's features for optimization and garbage collection. Originally it was written for the JVM (Java Virtual Machine). Hence it provides great inter-operability with Java and other JVM languages, including seamless integration with OOP features, and access to Java's huge library ecosystem.
Clojure code can also be compiled to Javascript via ClojureScript, hence it can be used as a full stack development language. Another implementation is ClojureCLR, targeting the .NET platform.
Clojure has been in stable release for several years, currently on version 1.10.1. Developer community and library ecosystem are improving rapidly, and the language is gaining adoption in large companies too, for example Walmart and Atlassian.
Rich Hickey, the language creator and BDFL is a feature himself. Just listen to his talks on Youtube and you'll see why.

To give a glimpse into the syntax, here is a sample code snippet that calculates the first few Fibonacci numbers. It is evaluated on the fly!

Hint: try changing the number after take.

; Fibonacci-series with lazy sequence
(def fib-seq
  ((fn fib [a b] 
     (lazy-seq (cons a (fib b (+ a b)))))
   0 1))
   
(take 15 fib-seq)

Don't worry if it looks Greek to you. A step-by-step tutorial will follow, presenting Clojure concepts with interactive examples. The next part is about Clojure syntax and data structures.

[Clojure] 01 Introduction