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diff --git a/doc/sphinx/language/core/variants.rst b/doc/sphinx/language/core/variants.rst index d9e2c07951..315e97687b 100644 --- a/doc/sphinx/language/core/variants.rst +++ b/doc/sphinx/language/core/variants.rst @@ -1,3 +1,55 @@ +Variants and the `match` construct +================================== + +Variants +-------- + +.. cmd:: Variant @variant_definition {* with @variant_definition } + + .. insertprodn variant_definition variant_definition + + .. prodn:: + variant_definition ::= @ident_decl {* @binder } {? %| {* @binder } } {? : @type } := {? %| } {+| @constructor } {? @decl_notations } + + The :cmd:`Variant` command is similar to the :cmd:`Inductive` command, except + that it disallows recursive definition of types (for instance, lists cannot + be defined using :cmd:`Variant`). No induction scheme is generated for + this variant, unless the :flag:`Nonrecursive Elimination Schemes` flag is on. + + This command supports the :attr:`universes(polymorphic)`, + :attr:`universes(monomorphic)`, :attr:`universes(template)`, + :attr:`universes(notemplate)`, :attr:`universes(cumulative)`, + :attr:`universes(noncumulative)` and :attr:`private(matching)` + attributes. + + .. exn:: The @num th argument of @ident must be @ident in @type. + :undocumented: + +Private (matching) inductive types +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. attr:: private(matching) + + This attribute can be used to forbid the use of the :g:`match` + construct on objects of this inductive type outside of the module + where it is defined. There is also a legacy syntax using the + ``Private`` prefix (cf. :n:`@legacy_attr`). + + The main use case of private (matching) inductive types is to emulate + quotient types / higher-order inductive types in projects such as + the `HoTT library <https://github.com/HoTT/HoTT>`_. + +.. example:: + + .. coqtop:: all + + Module Foo. + #[ private(matching) ] Inductive my_nat := my_O : my_nat | my_S : my_nat -> my_nat. + Check (fun x : my_nat => match x with my_O => true | my_S _ => false end). + End Foo. + Import Foo. + Fail Check (fun x : my_nat => match x with my_O => true | my_S _ => false end). + .. index:: match ... with ... Definition by cases: match |