Creating Polymorphic Types
Explore how to create and use polymorphic types in Haskell such as Maybe and Either for effective error handling. Understand how these types enable safer functions by representing optional values and computations that may fail without causing runtime errors. Learn to write polymorphic constructors and implement safe list operations by applying these concepts.
We'll cover the following...
So far, all the types that we created have been concrete types. But just like polymorphic functions, we can also create polymorphic types. We will study them in the context of types for better error handling.
The Maybe type
A polymorphic type is a type which contains one or more type variables. It can be seen as a recipe to create types by substituting the type variable with a concrete type.
As a first example, let’s look at the Maybe type from the Haskell Prelude that represents optional values. Its definition is
data Maybe a = Nothing | Just a
On the left side of the equation, there is the type variable a which can stand in for any type and can be used on the right hand side in the constructors. The Maybe type has two constructors:
Nothing, representing no valueJust,