[/
 / Copyright (c) 2008 Eric Niebler
 /
 / Distributed under the Boost Software License, Version 1.0. (See accompanying
 / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 /]

[/===============]
[section Glossary]
[/===============]

[def _T_ [~T]]

[template anchor[x] '''<anchor id="boost_proto.users_guide.glossary.'''[x]'''" />''']

[variablelist
  [ [ [anchor callable_transform] callable transform]
      [A transform of the form `R(A0,A1,...)` (i.e., a function type) where 
       `proto::is_callable<R>::value` is `true`. `R` is treated as a polymorphic 
       function object and the arguments are treated as transforms that yield the 
       arguments to the function object.] ]
  [ [ [anchor context] context]
      [In Proto, the term /context/ refers to an object that can be passed, along 
       with an expression to evaluate, to the `proto::eval()` function. The context 
       determines how the expression is evaluated. All context structs define a 
       nested `eval<>` template that, when instantiated with a node tag type (e.g., 
       `proto::tag::plus`), is a binary polymorphic function object that accepts an 
       expression of that type and the context object. In this way, contexts
       associate behaviors with expression nodes.] ]
  [ [ [anchor domain] domain]
      [In Proto, the term /domain/ refers to a type that associates expressions 
       within that domain with a /generator/ for that domain and optionally a 
       /grammar/ for the domain. Domains are used primarily to imbue expressions 
       within that domain with additional members and to restrict Proto's operator 
       overloads such that expressions not conforming to the domain's grammar are 
       never created. Domains are empty structs that inherit from
       `proto::domain<>`.]]
  [ [ [anchor dsel] domain-specific embedded language]
      [A domain-specific language implemented as a library. The language in which 
       the library is written is called the "host" language, and the language 
       implemented by the library is called the "embedded" language.]]
  [ [ [anchor dsl] domain-specific language]
      [A programming language that targets a particular problem space by providing 
       programming idioms, abstractions and constructs that match the constructs 
       within that problem space.]]
  [ [ [anchor expression] expression]
      [In Proto, an /expression/ is a heterogeneous tree where each node is either 
       an instantiation of `boost::proto::expr<>` or some type that is an extension 
       (via `boost::proto::extends<>` or `BOOST_PROTO_EXTENDS()`) of such an 
       instantiation.]]
  [ [ [anchor expression_template] expression template]
      [A C++ technique using templates and operator overloading to cause 
       expressions to build trees that represent the expression for lazy evaluation 
       later, rather than evaluating the expression eagerly. Some C++ libraries use 
       expression templates to build domain-specific embedded languages.]]
  [ [ [anchor generator] generator]
      [In Proto, a /generator/ is a unary polymorphic function object that you 
       specify when defining a /domain/. After constructing a new expression, Proto 
       passes the expression to your domain's generator for further processing. 
       Often, the generator wraps the expression in an extension wrapper that adds 
       additional members to it.]]
  [ [ [anchor grammar] grammar]
      [In Proto, a /grammar/ is a type that describes a subset of Proto expression 
       types. Expressions in a domain must conform to that domain's grammar. The 
       `proto::matches<>` metafunction evaluates whether an expression type matches 
       a grammar. Grammars are either primitives such as `proto::_`, composites 
       such as `proto::plus<>`, control structures such as `proto::or_<>`, or some 
       type derived from a grammar.]]
  [ [ [anchor object_transform] object transform]
      [A transform of the form `R(A0,A1,...)` (i.e., a function type) where 
       `proto::is_callable<R>::value` is `false`. `R` is treated as the type of an 
       object to construct and the arguments are treated as transforms that yield 
       the parameters to the constructor.]]
  [ [ [anchor polymorphic_function_object] polymorphic function object]
      [An instance of a class type with an overloaded function call operator and a 
       nested `result_type` typedef or `result<>` template for calculating the 
       return type of the function call operator.]]
  [ [ [anchor primitive_transform] primitive transform]
      [A type that defines a kind of polymorphic function object that takes three 
       arguments: expression, state, and data. Primitive transforms can be used to 
       compose callable transforms and object transforms.]]
  [ [ [anchor transform] transform]
      [Transforms are used to manipulate expression trees. They come in three 
       flavors: primitive transforms, callable transforms, or object transforms. A 
       transform `_T_` can be made into a ternary polymorphic function object with 
       `proto::when<>`, as in `proto::when<proto::_, _T_>`. Such a function object 
       accepts /expression/, /state/, and /data/ parameters, and computes a result 
       from them.]]
]

[endsect]
