Polymorphic functions

. Functions can be invoked with arguments of different types

. Built in operators for indexing arrays, applying functions, and manipulating pointers are usually polymorphic

. Extend type expressions to include expressions with type variables

. Facilitate the implementation of algorithms that manipulate data structures (regardless of types of elements)

- Determine length of the list without knowing types of the elements

In some circumstances, it is useful to write a function that can accept any data type for one of its parameters. Polymorphic functions facilitate the implementation of algorithms that manipulate data structures (regardless of types of elements).