How do you program differently in dynamic languages?

Question

How would someone who really knows how to take advantage of dynamic programming languages approach programming differently than someone working in a static language?

I'm familiar with the whole debate over static versus dynamic typing, but that's not what I'm getting at. I'd like to discuss problem solving techniques that are practical in dynamic languages but not in static languages.

Most of the code I've seen written in dynamic programming languages isn't very different than code written in static programming languages. As the saying goes, you can write FORTRAN in any language, and many people do. But some people use dynamic programming languages to solve problems in a way that wouldn't easily translate into, for example, C++. What are some of their techniques?

What are some good resources that discuss how to use dynamic programming languages? Not books on language syntax or API reference, but resources on problem solving approaches that take advantage of dynamic language capabilities.

EDIT (1/5/2009): I appreciate the answers below, but they don't seem to account for the huge increases in productivity that dynamic language advocates say they experience.

Answer 1

I like slim's answer. I do spend a crazy amount of time in Java and C++ crafting custom data structures that are just free in Python/Ruby. And crafting specialized functions to process these custom data structures. Yes, in C++, STL is really nice. Yes, Generics in Java are nice. They help create custom data structures much faster, however they still require a lot of thought and consideration.

However, there is a more fundamental reason why dynamic languages are easier to work with. It is a deep idea which is called duck typing. Some comments above refer to duck typing, but please take time to reflect on what duck typing is. It is a fundamentally different way to view the world. A view that is incompatible with languages like Java and C++.

Duck typing means that you waste not time in defining what a duck is. By not having to formally define your objects you save a lot of time and energy. Getting definitions right is hard. Have a look at this blog post of mine where I give examples: Formal definitions are less useful than you think

Duck typing has proven extremely useful. The "Must Ignore" principle in XML is what has made XML so significant and useful on the web. But that's just an instance of duck typing.

Another way to express duck typing is by the Web mantra "Be strict in what you send, generous in what you accept". That is also a very fundamental idea.

Finally, you may want to back to a long blog post of mine where I explain duck typing and how it relates to things like AI and modelling: Duck Typing, Artificial Intelligence and Philosophy

Answer 2

One way I typically find myself taking advantage of dynamic programming languages is in simplifying and clarifying syntax. If I'm representing a database, for example, the syntax I use for interacting with it can be much cleaner if I can dynamically load properties and methods on the database object for its tables, the tables and rows for their columns, and so on. The difference might be between:

$row = $db->getTable('user')->getRow(27); $row->setValue('name', 'Bob'); 

and

$row = $db->user->getRow(27); $row->name = 'Bob'; 

The 'visual noise savings' of the second form really starts to add up when you're doing complex things.