Running procedures while in a GUI

So I'm trying to make a crafting table,

All the procedures work fine, I have one that checks if the right items are in the right slots, and if they are the result of the crafting is put in the output slot, then I've got another the removes anything in the output slot if something is removed from the input slots, and then one last on the removes the items in the input slot if the item that is output is taken. 

The issue I'm having is that I can't run the first procedure all the time, only when the contents of the input slots are changed, so it doesn't run when I put an item in the slot

Is there any way of having a procedure constantly running while a specific gui is open? Or some other way of making this work like a normal crafting bench in minecraft?

Thanks in advance