Concept Expr

Description

An Expr represents a tagged node in an expression tree. The children of the Expr must themselves satisfy the Expr concept. The Expr has an arity representing the number of children. If the number of children is zero, the Expr also has a value. An Expr also has an associated Domain.

Associated types

proto_tag
```
Expr::proto_tag
```
The tag type of the Expr.
proto_args
```
Expr::proto_args
```
A typelist representing either the types of the child nodes, or, if the arity of the Expr is 0, of the value of the terminal.
proto_arity
```
Expr::proto_arity
```
The arity (number of child nodes) of the Expr. proto_arity is an MPL Integral Constant.
proto_grammar
```
Expr::proto_grammar
```
A typedef for an instantiation of proto::basic_expr<> that is equivalent to Expr. Expression types are equivalent if they have the same proto_tag, proto_args, and proto_arity.
proto_base_expr
```
Expr::proto_base_expr
```
A typedef for an instantiation of proto::expr<> or proto::basic_expr<> that is equivalent to Expr. Expression types are equivalent if they have the same proto_tag, proto_args, and proto_arity.
proto_derived_expr
```
Expr::proto_derived_expr
```
A typedef for Expr.
proto_domain
```
Expr::proto_domain
```
The Domain of the Expr. proto_domain models Domain.
proto_childN
```
Expr::proto_childN
```
The type of the Nth child of Expr. Requires 0 == N::value || N::value < proto_arity::value

Notation

Expr: A type playing the role of expession-type in the Expr concept.
Tag: A type playing the role of tag-type in the Expr concept.
Domain: A type playing the role of domain-type in the Expr concept.
N: A type playing the role of mpl-integral-constant-type in the Expr concept.
e: Object of type Expr

Valid expressions

Name	Expression	Type	Semantics
Get N-th Child	boost::proto::child< N >(e)	proto_childN	Extracts the Nth child from this Expr. Requires `N::value < proto_arity::value`.
Get Terminal Value	boost::proto::value(e)	proto_child0	Extracts the value from a terminal Expr. Requires `0 == proto_arity::value`.
Get Base	e.proto_base()	proto_base_expr	Returns an object of type `proto::expr<>` or `proto::basic_expr<>` that is equivalent to `e`.

Models

boost::proto::literal< int >