Procedures -- waiting and cross-tick

Hey, I'm still a total noob with procedures. I was wondering how I might have one re-occur every tick until a certain condition is fulfilled. (In my case, I'd like a block to damage the player whilst they attack it until they stop doing so.) The problem is, I'm not sure how to make a loop that waits one tick, or comes back to the procedure later. I know how to make a loop, but that will just lock the game up for the specified number of ticks.

If anyone knows how this works a little better than I do, I'd really appreciate some help.

Cheers,

~zxin