permColls

permColls refers to a set of data structures or algorithms designed for persistent collections. In computer science, persistence in data structures means that old versions of a data structure are preserved after updates. Instead of modifying a data structure in place, persistent data structures create new versions that share structure with the old ones, making it efficient to access and store previous states.

The term permColls is not a universally standardized technical term but likely describes collections that exhibit this persistent behavior. This contrasts with ephemeral data structures, where modifications overwrite previous states, making them inaccessible. Persistent collections are valuable in scenarios requiring historical tracking, undo/redo functionality, or concurrent access to different versions of data without interference.

Common implementations of persistent collections involve techniques like path copying. When a modification occurs, only the nodes on the path from the root to the modified element are copied. The rest of the structure is shared between the old and new versions. This sharing mechanism minimizes memory overhead and allows for efficient versioning. Examples of data structures that can be made persistent include lists, trees, and maps. The development of efficient persistent collections is a significant area within functional programming and theoretical computer science.