Generalized algebraic data type
A generalized algebraic data type is an algebraic data type whose constructors can impose more specific types on its type parameters.
Functional Design and Architecture: Examples in Haskell
A generalized algebraic data type is an algebraic data type whose constructors can provide more specific type information than the surrounding type declaration.
- How it is used
- Models API-like service operations and typed eDSL instructions whose constructors return different result types.
- How deep it goes
- Works through constructor-specific result types, interpreters, smart constructors, and locally quantified continuations; defers a formal type-system account.
- Examples
- Uses controller status and sensor requests, embedded Hdl scripts, and meteor and asteroid reporting operations.
- What you can do after
- Build it from scratch as a typed request interface, interpreter, and dependency-injected service runner.
Learn Haskell by Example
A generalized algebraic data type allows data constructors to specify more precise type information than ordinary algebraic data types.
- How it is used
- Uses constructor-specific types to recover precise information while processing polymorphic parsing and image data.
- How deep it goes
- Explains syntax, constructor-driven refinement, pattern matching, and existential composition, stopping short of broader implementation internals.
- Examples
- Demonstrates GiveMe values, typed PNM images, and conversion from 8-bit to 16-bit pixels.
- What you can do after
- Build it from scratch using GADTs to write type-safe polymorphic functions and dynamically store typed image values.
Read how Learn Haskell by Example explains generalized algebraic data type →
Related concepts
- algebraic data typekind of · An algebraic data type is a composite type whose values are formed from product structures, finite alternatives, or both through type constructors.
- free monadcontrasts with · A free monad represents computations as composable syntax over an operation set, with interpretation and execution supplied separately.
- StandaloneDerivingconfigured by · StandaloneDeriving is a GHC language extension that permits deriving clauses and type-class instances to be declared separately from data type declarations.
- type classcontrasts with · A type class is a language feature defining operations and constraints that types can satisfy to support ad hoc polymorphism.
- existential typeuses · An existential type hides a concrete type while exposing values and operations guaranteed by constraints on that type.
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