You could use bullet for the player.
For example,
> on left key down { set angle of motion to 180}
> on right key down { set angle of motion to 0 } and so on..
keep in mind you would have to have events for the on release as well that would stop the bullet movement
Firstly, nice pfp, secondly, that's what I tried first, but it was clunky and didn't move very smoothly. Also, it doesn't really work slippery-ly. I have tried working with momentum stuff but none of that really seemed to work.