I'm using it for scripting for a game engine. Its lazy evaluation feature allows me to define domain specific languages right inside the Io language, so for in

I'm using it for scripting for a game engine. Its lazy evaluation feature allows me to define domain specific languages right inside the Io language, so for instance I've used it to implement a syntax for declaring the properties of 3d objects (shape, color, position, type, etc.) that is inspired by cascading style sheets. It performs better than I expected - when I profile the code, Io is never the main consumer of the CPU; it is always the graphics first and secondarily the physics. Occaisionally I make a mistake in my binding library that makes the binding library itself consume too much CPU, but when I fix those bugs it goes back to profiling as the script using only about 4% - 5% of my CPU budget.