Introduction to Types and Typeclasses

• In Haskell, types and typeclasses are both key concepts, but they serve very different purposes.

Types

• A type defines a set of values and how data is structures in a program. It's essentially a way of classifying values into different kinds, such as Int, Bool, or user-defined.
• Types in Haskell are used to specify what kind of values functions can take as arguments and return as results.

Typeclasses

• A typeclass is more like an interface in other languages. It defines a set of functions that can operate on multiple types, but it doesn't specify the data structure itself.
• Instead, it defines behaviors or capabilities that a type must implement to belong to that class.
• The Eq typeclass in Haskell is an excellent example to help understand what a typeclass is and how it works.

Eq

• Eq is a typeclass in Haskell that defines equality for types.

• Any type that is an instance of the Eq typeclass must implement the equality function == and its complementary function /=

• In simpler terms, if a type is an instance of Eq, it means that values of that type can be compared for equality or inequality.

• In the following lectures we will define custom data types of our own. Moreover, we will see how we can make a type an instance of the Eq typeclass.