Iterators for ropes. It is more efficient to use an iterator to perform small steps and get the characters than to use Rope.get repeatedly.
Mutable iterator on a rope. Iterators are less efficient than Rope.get on small ropes (of length <= 1024 chars).
make r i0 returns a new iterator for the rope r. It is initially at position i0.
val get : t -> charget itr returns the character of the rope at the current position. O(1) time. This does not change the current position.
val peek : t -> int -> charpeek itr i returns the character i of the rope. If i is close to the current position of the iterator, this will in general be more efficient than get rope i.
val pos : t -> intpos itr returns the current position. It may not be a valid position of the rope. O(1) time.
val incr : t -> unitincr itr moves to the next character. O(1) time.
val decr : t -> unitdecr itr moves to the previous character. O(1) time.
val goto : t -> int -> unitgoto itr i move to position i. O(1) time but the next call to get may be slower.
val move : t -> int -> unitmode itr i move the current position by i chars (i may be negative or null). O(1) time but the next call to get may be slower.