@hackage sequential-index0.1

Sequential index numbers between 0.0 and 1.0 that allow arbitrarily inserting new numbers in between. They can possibly used for disk-based and other special containers, where adding a new element without changing the indexes of the other elements is important. Conceptually, SequentialIndex denotes a path to an element in an imaginary binary tree. However, leafs can only be on the right side of their parent. I.e. the path must end with a '1' (or be the path to the root node, 0.0). 1.0 denotes the invalid node.