The type must be a model of . It also models Unary Polymorphic Function.
The type must be a model of Expr

A Domain creates an association between expressions and a so-called generator, which is a function that maps an expression in the default domain to an equivalent expression in this Domain. It also associates an expression with a grammar, to which all expressions within this Domain must conform.

The grammar to which every expression in this Domain must conform.

A Unary Polymorphic Function that accepts expressions in the default domain and emits expressions in this Domain.

The Domain that is a super-domain of this domain, if any such domain exists. If not, it is some unspecified type.

The type of the result of applying `proto_generator` to the specified expression type. The result is required to model Expr. The domain type associated with `result_type` (`result_type::proto_domain`) is required to be the same type as this Domain.

The result of converting some type to a Proto expression type in this domain. This is used, for instance, when calculating the type of a variable to hold a Proto expression. `as_expr_result_type` models `Expr`.

The result of converting some type to a Proto expression type in this domain. This is used, for instance, to compute the type of an object suitable for storage as a child in an expression tree. `as_child_result_type` models `Expr`.

The result of applying `proto_generator` to the specified expression.
The result of converting some object to a Proto expression in this domain. It returns a Proto expression object that is suitable for storage in a variable. It should return a new object, which may be a copy of the object passed in.
The result of converting some object to a Proto expression in this domain. It returns an object suitable for storage as a child in an expression tree, which may simply be a reference to the object passed in.