passing "var addr x" into procedure

[PMunch]

In general Nim will do "the right thing" when passing objects around. If an 
object is small enough it will be passed by value, if it's above a certain size 
it will pass a pointer instead so that you don't copy the data everywhere. This 
is an optimisation which is tuned for speed, and in general you shouldn't have 
to think about how objects are passed around.