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## Concept Domain

Domain

## Description

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.

## Associated types

- proto_grammar

      Domain::proto_grammar

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

- proto_generator

      Domain::proto_generator

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

- result_type

      boost::result_of<Domain(Expr)>::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` is required to be the same type as this Domain.

## Notation

Domain
  A type playing the role of domain-type in the Domain concept.
Expr
  A type playing the role of expression-type in the Domain concept.
`d`
  Object of type Domain
`e`
  Object of type Expr

## Valid expressions

Name | Expression | Type | Semantics
--- | --- | --- | ---
Apply Generator | d(e) | result_type | The result of applying `proto_generator` to the specified expression.

## Models

- boost::proto::default_domain