Supervisor modes

I changed operations so that it can be applied to replicated nodes, including bind, read, next, wait_needed, is_det, declare. There are still two operations 'fetch'  and 'reply_fetch' to be done. They are used to fetch values when a dataflow variable is bound to another.
I am fixing them and replacing most if by case. However, for conditions like
if lenght(X) >0
I don't know if it is better to change it to case.