Pre-Collision Detection question

[crapgarden]

FYI - I'm coding in actionscript 3.0 but didn't see an area to post for that language.

I made a simple character and a block. I'm trying to get it so that if the character will touch the box, it wont let him move to imply a wall/collision.

I've got him moving but the problem is that it doesn't PREdetect the collision. It lets him overlap the block once, then when I try to move again, it wont go anywhere because NOW (that it's too late), he's overlapping and thus colliding. Anyone know how I can very simply edit this code so the player isn't allowed to overlap the block in the first place?

import flash.display.Sprite;
import flash.events.KeyboardEvent;

var block:Sprite = MovieClip(blockInst);
var player:Sprite = MovieClip(playerInst);
var speed:Number = 10;

stage.addEventListener(KeyboardEvent.KEY_DOWN, playerMovement);

function playerMovement(key:KeyboardEvent):void
{
	if (player.hitTestObject(block))
	{
		trace("blocked");
	}
	
	else
	{
		switch (key.keyCode)
		{
			case 37 ://Left
				player.x -=  speed;
				break;

			case 39 ://Right
				player.x +=  speed;
				break;

			case 38 ://Up
				player.y -=  speed;
				break;

			case 40 ://Down
				player.y +=  speed;
				break;
		}
	}

}

[firstPerson]

Yea so this is a problem of collision response. Once a collision is detected what do you do? Well in this case you should move your player back just before the collision point. So if there is a collision, shift back the player's position so that there is not a collision anymore. Get it?