Messaging as a programming model

This is worth reading.

Monads made difficult

I still really haven't got a clue what a monad is. This didn't help.

Don't check - tell, in Ruby

Here's a neat idiom: instead of checking for a null pointer return, use a do construct in Ruby to either act on the return or not (if it's null). Very slick and elegant.

Promises.

What promises are and how they're used.

Combinators presented well

This may well be the most salient article I've ever seen explaining why combinators are a useful tool.  Raganwald is a pretty hoopy frood.

"Either" in C#

Here's a neat little article about implementing a variant "either" structure (this is a feature of Haskell that permits a flag in a structure to switch between two subtypes) in C#.

Don't repeat yourself

DRY.  I'd seen it bandied about.  It's a good principle - but essentially it's one that you can only implement in LISP or another macro-enabled language.

Python productivity

One of Python's key features is its simple expression of some very cogent mental structures.  Here's a nice short article on that:

• Dictionary and set comprehensions
• Counter objects
• JSON pretty printing
• Quick and dirty Web service

(Note that I've construed the article a little differently from its author's intent.)

Programming language social mores

The ever-entertaining Zed Shaw writes about the realization that what are often called programming language "idioms" are actually social mores used as community membership signifiers.

Python idioms

Here's a nice rundown of some Pythonic idioms. The interesting thing about idioms between languages is that they syntactically encode the same (or similar, or sometimes congruent) mental/semantic structures about what the code is supposed to do.

That deserves thought.