Moving point along line

Having a complete brain fart here but looking for a way to take a point, constrain it to a line, and make it only able to move along that line.  I started out with two rhino points (for begnning and ending point of line) then used the grasshopper 2point line component to make the line.  Now I am not sure how to constrain the point to the line and set it to move along that line; my intentions are to use this point later an attractor point.