Personally, I'd check for a potential collision just before an object is about to move - and if a collision is about to happen, either not move, or do whatever you do if objects collide. That way, you don't have to move an object, cascade any triggered actions, and then roll-back if the collision detection routine afterwards determines the move shouldn't have happened.

But then, that's just me. I also think your question has nothing to do with Perl. You'd face the same problems if you would program your game in C, Java or Python. You'd better off asking in a forum that's about game programming. There you have a much better chance of meeting someone who has tackled this problem before.

Abigail