The latest release of CoffeeScript has a new ‘literate’ mode to make it easier to develop Markdown documents that are executable.

CoffeeScript is a small language that compiles into the equivalent JavaScript with no interpretation at runtime.

It is described by the developers as an attempt to expose the good parts of JavaScript in a simple way. You can use any existing JavaScript library seamlessly from CoffeeScript, and the compiled output remains readable, passes through JavaScript Lint without warnings, will work in every JavaScript runtime, and tends to run as fast or faster than the equivalent handwritten JavaScript.

The ‘Literate Programming’ mode is optional, and is used to make code more readable. If a file is marked as ‘.litcoffee’. then when the compiler is compiling it to JavaScript, anything that isn't indented is discarded, and only the indented text is compiled.

This means that Markdown code results in an output file that can be completely compiled, because in Markdown indenting is used to denote source code. Markdown is a text-to-HTML conversion tool for web writers. It allows you to write in plain text format, then convert it to structurally valid XHTML (or HTML).

The output can also be used to create formatted documents, and can be displayed in editors with syntax highlighting. The announcement about the new feature on the CoffeeScript website says that as 1.5.0 is the first version of CoffeeScript that supports literate programming, they’d like to know if you have any ideas for improving the feature.

The other main changes to the new version are a move to the Node.js Read-eval-print-loop (REPL) format, support for negative loop counters to work through arrays backwards, and disallowing the return of values from constructors.