Parametric Slide

Customize this slide and carriage to your own specification, just 4 parameters to alter.
This is only my second attempt at writing script in OpenSCAD so still learning.
I have made a small one as a test. (see photo)
I printed the slide first then the carriage with a 0.2 mm gap which fitted okay but was a bit sloppy so I printed another with a 0.1 gap and that was a nice fit.
I would like to add some bolt holes for attaching things and possibly the option to add a locking device to the carri