• Schola: A social network for Latin speakers.

• The Ultimate Commodore 64 Talk @25C3: Commodore 64 in a nutshell. (Well, a sizable nut…)

• How to create custom icons for your Mac: Useful.

• Functional programming languages (lectures): Heavy stuff.

• G3 icons for Adium: How cool is that? :-)

What this word actually means is a technique where you take a number of values, process them in some way, and end up with fewer values (often a single one). A good example would be, computing the sum of a list of numbers.

In Python, one way to do this used to be using reduce (and that still works, but has been superseded by the sum built-in). Using this approach actually illustrates the concept well, known as folding in functional languages.

>>> numbers = [3, 6, 8, 12, -5]
>>> reduce(lambda x, y: x+y, numbers)
24

In other words, a catamorphism is just a fold. Oh, and the opposite (an “unfold”) is called an anamorphism.

That’s really all there is to it. (Of course, folding can and does get much more complex, but that’s a different story.)