What is the idiomatic Ruby way to go through all the elements of an array,
except the last one, gettting the index?

my_array.each_index {
    |i|
    unless i == my_array.last {
        # ...
    }
}

seems less than neat.

Reason I want to do this -- If one is producing a difference table from an
array such that: 
    d[i] = a[i+1] - a[i]
one doesn't want to fall off the end...

	Hugh