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HC10-10. Haskell Chapter 10 Practical Tasks: Creating-Type-Classes-and-Instances |
This topic explores creating type classes and instances in Haskell, allowing developers to define reusable behavior across multiple types. It begins with overloading, explaining how type classes enable polymorphic functions. The step-by-step process of defining a type class is introduced using the Eq type class, followed by creating multiple instances for different types. The lesson then demonstrates how to improve Eq using mutual recursion and the mathematical concept of the greatest common divisor (MCD). A key challenge—defining an instance for a parameterized type—is covered, ensuring flexibility in type definitions. Two example type classes, WeAccept and Container, illustrate how custom type classes can model real-world concepts. The lesson also explores the Ord type class, introducing subclassing, where one type class depends on another. Finally, the deriving mechanism is explained, showing how Haskell can automatically generate instances, along with pitfalls where deriving can go wrong. By mastering these concepts, developers can create powerful abstractions and write more reusable, maintainable Haskell code. |
