Chapter 12 Language extensions

10 Generalized algebraic datatypes

Generalized algebraic datatypes, or GADTs, extend usual sum types in two ways: constraints on type parameters may change depending on the value constructor, and some type variables may be existentially quantified. They are described in chapter 7.

(Introduced in OCaml 4.00)

constr-decl	::=	...
	∣	constr-name : [ constr-args -> ] typexpr

type-param	::=	...
	∣	[variance] _

Refutation cases. (Introduced in OCaml 4.03)

matching-case	::=	pattern [when expr] -> expr
	∣	pattern -> .

Explicit naming of existentials. (Introduced in OCaml 4.13.0)

pattern	::=	...
	∣	constr ( type { typeconstr-name }⁺ ) ( pattern )