Parametricityyppiin
Parametricityyppiin, often shortened to parametricity, is a fundamental concept in programming language theory, particularly within statically typed functional languages. It describes a property that holds for universally quantified types. In essence, parametricity states that a function with a polymorphic type should behave uniformly regardless of the type of the values it operates on. This means that a function like `id :: forall a. a -> a` (the identity function) cannot inspect the type of its argument. If it receives an integer, it must return an integer. If it receives a string, it must return a string. It cannot, for instance, behave differently based on whether the argument is a primitive type or a complex data structure.
The principle of parametricity, often referred to as the abstraction of types, implies that polymorphic functions
This property is not just a theoretical curiosity; it has significant practical implications for program design