Clojure

One parting thought is that I have come to think of Clojure as sort of a data structure oriented functional programming.

Assuming your new function is written in terms of Clojure's built-in functions, it will automatically be able to support all the same types.

However, like any other language, we need to set up a development environment for working with it.

Clojars is a new repository that aims to make it easy to share and consume Clojure libraries.

Making a basic linked-list data structure persistent is the easiest exercise; here, a list in Clojure is bound to a var named "a"

The other side of the medal is of course a matter of dependencies: using Clojure means another new dependency to a project.

Agents are an important feature in Clojure and it's nice to see them show up in GPars.

The cells where these rows and columns intersect represent existing implementations of these functions provided by Clojure.

The other part that is built in Clojure is all the statistical inference and machine learning code.

Agents are used in Clojure (see Resources) to coordinate multithreaded access to an identifiable piece of changing state.

Unlike the Java language, Clojure requires this to be declared as an explicit argument to the function.

Clojure Protocols: Take a look at slides presented by Stuart Halloway at the International Software Development Conference 2010.

One of the benefits of Clojure as a Lisp variant is that code is data (also known as homoiconicity).

Each of the keys in the map is a Clojure keyword, which always evaluates to itself and is identical to the same keyword used anywhere else.

Notice that datatypes can implement methods of any Java interface, not only those generated by Clojure protocols.

Later in this article, I'll demonstrate both an object-oriented implementation in Java code and a functional variant in Clojure.

This function starts with the Clojure special form loop, which creates a target for the recur at the end of the function.

Structural sharing is the technique used to make Clojure's persistent data structures efficient.

A macro allows you to extend the Clojure compiler to essentially add new keywords to the language.

Clojure does offer different styles of runtime polymorphism, for instance in the form of multimethods.

Now that we have the basic setup out of the way, let's explore the language by writing some Clojure programs.

We use Clojure data structure literals as both intermediate representation for communication, and for storage.

Clojure provides a core set of persistent, immutable data structures: lists, vectors, maps, sets, and queues.

The Clojure core API contains an elegant zipper implementation in clojure. zip, with the API shown in Listing 11.

Two main parts of the system are written in Clojure.

It converts keys in the map entries of JSON objects to Clojure keywords, which are more idiomatic to work with in Clojure.

The ClojureScript compiler contains no Javascript code, it's written in Clojure, which means the compiler needs to run on a Java VM.

For instance, normal Clojure functions have low call overhead as they're mostly reduced to static method calls.

The Fibonacci numbers form an infinite sequence, so it should be described as such using Clojure's infinite lazy sequences.

Whether it's a good idea to add another, still little known, language like Clojure to a project, is a question every team has to answer.

With clojure-dev, you get some basic syntax highlighting, including parentheses matching (a must-have for any Lisp).

If you print a map you'll see commas between map entries, but it's purely for readability; commas are treated as whitespace in Clojure.

So far, we have achieved almost the same level of essential complexity as with the clojure. walk implementation in Listing 10.

Clojure has already compiled the protocol you defined earlier into JVM bytecode representing this interface.

Our challenge now is to take a tree of Clojure maps and traverse or manipulate it.

Download core. match: An optimized pattern-matching and predicate-dispatch library for Clojure.

This article covers the use of Clojure for performing basic CouchDB operations, querying CouchDB using views, and database replication.

There are many different concurrency problems out there, but many of them will map nicely to one of Clojure's models.

In fact, recently, a number of new languages like Scala, Clojure, and F# have evolved, all promising to simplify concurrency.

Clojure: Visit the Clojure website and check out the Protocols and Datatypes pages.

Here, the columns represent functions in Clojure's standard collection API: conj, nth, empty, and count.

You can find some examples of this in the core Clojure API's more advanced macro utilities.

In Clojure, a multimethod is a special kind of function that breaks invocation into two steps.

Finally, Clojure is a language designed with concurrency in mind and has some unique features related to concurrent programming.

Another option is to use Clojure for performance bottlenecks.

Clojure favors uniform interfaces, so it encourages storing structured data in maps.

It originally supported only Ruby, but has since expanded to cover node. js, the JVM-based Clojure, and now Java.

Clojure libraries inspired by Ruby libraries are one way the two languages interact.

Clojure is a LISP and comes with a powerful macro system.

Rows represent classes (Java) and datatypes (Clojure) that already exist.

Clojure's Solutions to the Expression Problem: View video and slides from a presentation by Chris Houser at Strange Loop 2010.

We also need a zipper implementation that can deal with the standard Clojure data structures during traversal.

Being a functional language, Clojure brings new tricks to data query and manipulation.

Similarly, the rows represent Clojure's built-in collection types: list, vector, map, and set.

First we use the str function from Clojure to convert the char to a string.

One other important aspect of Clojure is its tight integration with the Java language.

The Listing 1 example defines Clojure functions named invoice and manifest, both living in the com. amalgamated namespace.

This is not an introductory article to Clojure, so some familiarity with it is assumed.

You start to talk to them about Clojure, Lisp, and the Expression Problem, and their eyes glaze over.

Clojure is a possible solution for this problem: the language has various levels of flexbility.

But then another team of Java-only developers needs to build another invoice generator that is compatible with your Clojure code.

Here, we take advantage of Clojure's support for multi-line strings.

The examples are written from the perspective of coding at the Clojure REPL.

This follows Clojure naming conventions.

If you want to change state in a way that other threads will see it, then you might want to use Clojure's atoms.

To fill that role, Clojure offers a variant of datatype for things that aren't records.

Eclipse users can install the clojure-dev plug-in using its Eclipse update site.

With just these two simple examples, we have seen many features of Clojure.

Clojure is fundamentally different in all respects.

Clojure's refs provide its most powerful flavor of concurrency.

This article has shown you each of Clojure's concurrency models.

Clojure is a highly experimental language that's making inroads into industry, which is pretty rare.

Second, you're confined to running the query only via your Clojure code.

This is where newer, more modern programming languages come into play, and Clojure is a great example.

In fact, every Clojure protocol is also a Java interface with the same name and methods.

All in all, Clojure offers a lot of opportunities to write fast code in an elegant style.

I am sure that sometime soon we will have ML style pattern matching in Clojure, people have already been working on implementations.

Listing 1 shows a simple example of using vars in Clojure.

The key to using Clojure's STM is wrapping things inside the dosync function.

Clojure's core API includes a library, clojure. walk, that is specifically for traversing data structures.

Clojure is built around these ideas.

This is a common pattern, and Clojure provides a programming model to address this: agents.

The ability to write CouchDB views in Clojure means you have one less language to support in an application and more continuity in the code.

Go to the Clojure site to download Clojure, read tutorials, and access reference documentation.

This aspect of Clojure has always bothered me because I'm so steeped in state-based thinking.

The HTTP-based examples I'll show use clojure. contrib. json.

There are two common ways to develop and run Clojure programs.

These classes implement their own generic interfaces, so it doesn't make sense for them to behave like Clojure maps.

InfoQ: Could you give a short overview of how your Clojure code is structured?

This tells Clojure to de-reference the pointer and gives you the actual value.

The Java world is showing a lot of interest now in functional languages such as Scala and Clojure.

The number 1 tip for working with Clojure libs is that Clojure-core and Clojure-contrib are small, so go read all the code.

This is variable assignment in Clojure.

InfoQ: You mentioned Clojure readers for importing data formats toClojure data structures; do you use Reader macros?

For this article, Eclipse V3. 5 was used, along with clojure-dev 0. 0. 34.

Now you have solved several problems while learning how to use Clojure at the same time.

Listing 4 is a JSON document (from CouchDB) followed by an equivalent Clojure map representation

It remains to be seen how chunked sequences are received; they obviously have advantages, but as the Clojure 1. 1 Changes file points out