Polymorphic recursion

Polymorphic recursion exists in a data structure when the data structure is recursive, and it uses generics for the recursion, and it is recursing on itself with a different generic type.

In some strongly typed languages, such as C++, polymorphic recursion is difficult to implement because all data types are determined during compilation. Polymorphic recursion causes data types to be infinitely nested, forcing the compiler to throw an error.