[[wp:Parametric Polymorphism|Parametric Polymorphism]] is a way to define types or functions that are generic over other types. The genericity can be expressed by using ''type variables'' for the parameter type, and by a mechanism to explicitly or implicitly replace the type variables with concrete types when necessary.


;Task:
Write a small example for a type declaration that is parametric over another type, together with a short bit of code (and its type signature) that uses it.


A good example is a container type, let's say a binary tree, together with some function that traverses the tree, say, a ''map''-function that operates on every element of the tree.

This language feature only applies to statically-typed languages.
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