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Daniel Janus’s blog

Combining virtual sequences
or, Sequential Fun with Macros
or, How to Implement Clojure-Like Pseudo-Sequences with Poor Man’s Laziness in a Predominantly Imperative Language

9 December 2011

Sequences and iteration

There are a number of motivations for this post. One stems from my extensive exposure to Clojure over the past few years: this was, and still is, my primary programming language for everyday work. Soon, I realized that much of the power of Clojure comes from a sequence abstraction being one of its central concepts, and a standard library that contains many sequence-manipulating functions. It turns out that by combining them it is possible to solve a wide range of problems in a concise, high-level way. In contrast, it pays to think in terms of whole sequences, rather than individual elements.

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Color your own Europe with Clojure!

11 July 2011

This is a slightly edited translation of an article I first published on my Polish blog on January 19, 2011. It is meant to target newcomers to Clojure and show how to use Clojure to solve a simple real-life problems.

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Meet my little friend createTree

8 July 2011

I’ve recently been developing an iPhone application in my spare time. I’m not going to tell you what it is just yet (I will post a separate entry once I manage to get it into the App Store); for now, let me just say that I’m writing it in JavaScript and HTML5, using PhoneGap and jQTouch to give it a native touch.

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A quirk with JavaScript closures

15 May 2011

I keep running into this obstacle every now and then. Consider this example:

> q = []
> for (var i = 0; i < 3; i++)
    q.push(function() { console.log(i); });
> q[0]()

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The Dijkstran wheel of fortune: SPSS, Excel, VBA

28 March 2011

It is practically impossible to teach good programming to students that have had a prior exposure to BASIC: as potential programmers they are mentally mutilated beyond hope of regeneration.

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Hello world, again

11 March 2011

I’ve been quiet on the front of blogging in English recently. But that doesn’t mean I’ve given up.

After more than a year, I had become tired of maintaining a Blosxom installation. I greatly admire Blosxom, its minimalism and extensibility, but the default installation is just too minimal for my needs. And the plugins tend to have rough edges. Like the Disqus comments that I’ve enabled at one time on the otherwise static blog pages: the correct number of comments appears in some places but not all; besides, they just don’t feel right.

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Last post here

10 March 2011

I’ve decided to move my English blog to Posterous. The new address is This URL ( will point to the new blog in about a week’s time.

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Keyword arguments

4 May 2010

There’s been an ongoing debate about how to pass optional named arguments to Clojure functions. One way to do this is the defnk macro from clojure.contrib.def; I hesitate to call it canonical, since apparently not everyone uses it, but I’ve found it useful a number of times. Here’s a sample:

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18 April 2010

The program I’ve been writing about recently has come to a point where I think it can be shown to the wide public. It’s called Sunflower and has its home on GitHub. It’s nowhere near being completed, and of alpha quality right now, but even at this stage it might be useful.

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A case for symbol capture

5 April 2010

Clojure by default protects macro authors from incidentally capturing a local symbol. Stuart Halloway describes this in more detail, explaining why this is a Good Thing. However, sometimes this kind of symbol capture is called for. I’ve encountered one such case today while hacking a Swing application.

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