Interactive Development with Clojure.spec

clojure.spec provides seamless integration with clojure.test.check's generators. Write a spec, get a functioning generator, and you can use that generator in a REPL as you're developing, or in a generative test.

To explore this, we'll use clojure.spec to specify a scoring function for Codebreaker, a game based on an old game called Bulls and Cows, a predecessor to the board game, Mastermind. You might recognize this exercise if you've read The RSpec Book, however this will be a bit different.

Works On My Machine: Understanding Var Bindings and Roots

When designing applications and systems it can be important to understand the inner workings of certain aspects of the language being used by developers. One area of Clojure that is traditionally rather opaque and poorly understood is the inner workings of Vars, and how they interact with the Clojure Language. I recently encountered some behavior that seemed puzzling:

Focus on spec: Combining Specs with `and`

Clojure's new spec library provides the means to specify the structure of data and functions that take and return data. In this series, we'll take one Clojure spec feature at a time and examine it in more detail than you can find in the spec guide.

In our last post, we explored the simplest specs: predicate functions and sets. In this post we'll look at how you can start to combine specs using the and spec.

The New Normal: Tempo, Flow, and Maneuverability

Tempo. Most people are familiar with it in the musical sense. It’s the speed, cadence, rhythm that the music is played. It drives the music forward - and pulls it back.

But there’s more to tempo than a musical beat. In life, as author Venkatesh Rao described in his book, “Tempo,” it makes for some of the most memorable moments as it shifts faster or slower. In war, like in business, tempo - the speed at which you can transition from one task to the next - is a critical component for victory.

Welcome to

We are happy to announce that ClojureScript now has an official web site at! Most of the content from the ClojureScript wiki has been migrated into the new site and organized. 

The site design was carried over from the Clojure web site - thanks to Tom Hickey for the design on the original site. We have adopted the community CLJS logo as the official logo for ClojureScript - many thanks to the designers Chris Oakman and Brett Darnell. 

The new site content is hosted in a GitHub repository and is open for contributions. All contributions require a signed Clojure Contributor Agreement. This repository will accept contributions via pull request and issues with GitHub issues. The contribution and review process is described in more detail on the site contribution page.

This site is a starting point. Because most of the content originated in the wiki, it's likely to need updates in a number of places. There are also many places that content can be added in the Reference, Tools, Guides, and Community sections. We welcome your contributions and thank you for being part of the ClojureScript community! If you have questions, please file an issue on the site repo or contact us on the mailing lists, Slack, IRC, etc for discussion.

We look forward to seeing the site grow!

The New Normal: Mean Time To Reaction

Slime mold can teach you everything you need to know about being an agile, adaptive and responsive company.

OK, maybe not everything, but there are some valuable lessons to take away. That oozing organism can quickly sense, decide and act in response to changes in its environment.  It is no more than a group of amoebae encased in slime, yet they exhibit behaviors that are comparable to those of animals who possess muscles and nerves – that is, simple brains.