Theory

Algebraic Data Types (ADTs) build complex data from sums and products.

📦 Product Types combine fields (logical and).
🔀 Sum Types choose between constructors (logical or).
🌳 Recursive Types reference themselves.
🌀 Polymorphic Data abstracts over element types.

Expressiveness

Tuples, lists, Maybe, Either, user trees—all ADTs.

Example

data Result a
  = Success a
  | Failure String

Note

Pattern matching + compiler exhaustiveness = strong invariants.

Implementation

Define once, then use in pattern matches, derive instances:

data Color = Red | Green | Blue
  deriving (Eq, Show)

Deriving saves boilerplate for Eq, Ord, Read, Show, etc.