Hi all,
I've just finished up the first version of my Tween egg. It provides a (loose) port of Tween.js for Scheme. The functionality that tracked tween state is not present, as I felt that's better left to the client of the API and wasn't very much in the tradition of scheme, but otherwise it's functionally intact.
For those unaware, tweening is the action of 'inbetweening' two values; of which the popular linear interpolation is a common action. This egg provides a whole suite of interesting tweens, including the classic lerp.
It also provides linear, bezier, and catmull-rom interpolation functions.