First-class citizen
| Concept | Description | Languages |
|---|---|---|
| first-class function | closures and anonymous functions | Scheme, ML, Haskell, F#, Scala, Swift, PHP, Perl 6, JavaScript, Delphi |
| first-class control | continuations | Scheme, ML, F# |
| first-class type | Coq, Idris | |
| first-class data type | Generic Haskell. C++11 | |
| first-class polymorphism | impredicative polymorphism | |
| first-class message | dynamic messages (method calls) | Smalltalk,[8] Objective-C[8] |
| first-class class | metaclass | Smalltalk, Objective-C, Ruby, Python, Delphi |
| proof object[9] | Coq, Agda |