Derive Class Instances Topdown and Derive TTG Automatically

Learn advanced Haskell deriving mechanisms in this 24-minute conference presentation from the Haskell 2025 symposium. Explore a novel topdown approach to deriving class instances that generates multiple related instances simultaneously, addressing two common boilerplate scenarios: composite and nested data types requiring individual deriving clauses, and data types needing derivation for classes with multiple superclasses. Discover how to automatically transform regular data types into decoratable types using type families and Template Haskell, extending constructors to support the Trees That Grow (TTG) pattern. Master techniques that reduce repetitive deriving declarations and streamline instance generation for complex type hierarchies in functional programming.