A rope is a persistent data structure to represent text. Many languages contain built-in notions of text as strings or contiguous arrays of characters. In contrast, ropes are a tree-based representation of text. A key advantage of ropes is improved running times for common operations, such as concatenation and subsequence, compared to contiguous character arrays.

Some variations of ropes use self-balancing trees or support explicit balance operations. However, for these questions, we will consider a simple variation of ropes without any balancing operations. Such an unbalanced rope will be either:
- a string-i.e., an array of characters - and the length of the string;
- or a left rope, a right rope, and the total size of the two subropes.

Define the type for a rope as a variant. Assume that a type for strings (string) already exists.