Using Immutable Data Structures to Represent Binary Trees

Using immutable data structures or whatever to represent as an internal representation for binary trees is probably a very terrible idea. A pure function is exactly the same thing as a hash map, but it's just a map between input and output. It has nothing to do with the code of the load mathematically. There is no code of the function. Sinus X is not the code that calculates the sinus mathematically.