Lambda the Ultimate

F# 3.0 has a new feature called Type Providers:

An F# type provider is a component that provides types, properties, and methods for use in your program. Type providers are a significant part of F# 3.0 support for information-rich programming. The key to information-rich programming is to eliminate barriers to working with diverse information sources found on the Internet and in modern enterprise environments. One significant barrier to including a source of information into a program is the need to represent that information as types, properties, and methods for use in a programming language environment. Writing these types manually is very time-consuming and difficult to maintain. A common alternative is to use a code generator which adds files to your project; however, the conventional types of code generation do not integrate well into exploratory modes of programming supported by F# because the generated code must be replaced each time a service reference is adjusted.

This feature opens the door to some interesting applications, see for example the generation of vector types.