Some functions like "sol.main.get_angle(x1, y1, x2, y2)" work in radians. However, the circle movements work in degrees (initial angle, angle speed, etc). This is too confusing. All of these functions should use the same angle unit, and I personally prefer radians, although other people (like kids) may prefer degrees.

The best option could probably be to add another parameter (an optional parameter if you prefer) on each of these functions to indicate if we are using degrees or radians as angle unit. That is, if "unit" is one of the strings in the list {"degrees", "radians"}, we would write:

sol.main.get_angle(x1, y1, x2, y2, unit)
circle_movement:get_angle_speed(unit)
circle_movement:set_angle_speed(angle_speed, unit)

etc. And the same for all functions in the Lua API that use angles or angle speeds.