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10.10 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 )  
 

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