The point of 'bind_len' in 'term.ml'

[Yuting Wang]

In 'term.ml', there is a mutable variable named 'bind_len' which I think stores the length of 'bind_state'.

Since we can get the length of 'bind_state' using 'List.length'. What is the point of having 'bind_len'? 

If my understanding is correct, we should remove this variable since it causes unnecessary confusion.