Type class
A type class is a language feature defining operations and constraints that types can satisfy to support ad hoc polymorphism.
Learn Haskell by Example
A type class defines a set of operations and laws that types can implement to support ad hoc polymorphism.
- How it is used
- Generalizes operations in graph lookup, CSV handling, property tests, and music generation.
- How deep it goes
- Defines classes, instances, and constraints through Eq, then builds custom conversion and performance abstractions.
- Examples
- Uses associative-list membership, pitch-to-frequency conversion, performance playback, and generic random property tests.
- What you can do after
- Build it from scratch by declaring capabilities, implementing instances, and constraining generic Haskell functions.
Functional Design and Architecture: Examples in Haskell
A type class is a language feature that defines a common interface of operations and permits implementations for different types.
- How it is used
- Defines functional interfaces for service handlers, typed databases, and selectable service implementations.
- How deep it goes
- Explains classes and instances through handler and database code, then notes advanced extensions and expressiveness limits.
- Examples
- Uses sensor and controller handlers, named databases, and HTTP-versus-TCP reporting services.
- What you can do after
- Apply type classes to require capabilities and select implementations without exposing concrete representations.
Read how Functional Design and Architecture: Examples in Haskell explains type class →
Functional Programming in Scala, Second Edition
A typeclass is an abstraction that provides operations for types satisfying a specified interface or set of laws.
- How it is used
- Uses type classes to generalize functions across types while keeping type-specific operations in separate instances.
- How deep it goes
- Explains traits, canonical instances, context parameters, given resolution, and explicit instance selection through Monoid examples.
- Examples
- Demonstrates integer addition, integer multiplication, strings, Boolean conjunction, Boolean disjunction, list folding, and foldMap.
- What you can do after
- Apply type classes via Scala traits, givens, context parameters, foldMap, and explicit using arguments.
Read how Functional Programming in Scala, Second Edition explains type class →
Related concepts
- foldableincludes · Foldable is a typeclass abstraction for data structures whose elements can be traversed and reduced to a result by folding operations.
- Haskellused by · Haskell is a statically typed, purely functional programming language with non-strict, typically lazy evaluation.
- exceptionincludes · An exception is a runtime signal or object representing an abnormal condition that interrupts ordinary program flow and may be handled or propagated.
- enumincludes · An enum is a type or language construct whose values are selected from a finite set of named alternatives, which may carry associated data.
- MonadFailincludes · MonadFail is a Haskell type class that defines how pattern-match failure is represented within a monadic computation.
- type-level designkind of · A software design technique that encodes behavioral constraints and correctness conditions in types so the compiler can check them.
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