Make any Proto expression a valid Fusion sequence A PolymorphicFunctionObject type that returns a "flattened" view of a Proto expression tree. A PolymorphicFunctionObject type that returns a "flattened" view of a Proto expression tree. For a tree with a top-most node tag of type T, the elements of the flattened sequence are determined by recursing into each child node with the same tag type and returning those nodes of different type. So for instance, the Proto expression tree corresponding to the expression a | b | c has a flattened view with elements [a, b, c], even though the tree is grouped as ((a | b) | c). proto::callable This(Expr) proto::result_of::flatten< typename boost::remove_reference< Expr >::type > typename proto::result_of::flatten< Expr const >::type Expr const & A PolymorphicFunctionObject type that invokes the fusion::pop_front() algorithm on its argument. A PolymorphicFunctionObject type that invokes the fusion::pop_front() algorithm on its argument. This is useful for defining a CallableTransform such as pop_front(_), which removes the first child from a Proto expression node. Such a transform might be used as the first argument to the proto::fold<> transform; that is, fold all but the first child. proto::callable This(Expr) fusion::result_of::pop_front< typename boost::remove_reference< Expr >::type const > typename fusion::result_of::pop_front< Expr const >::type Expr const & A PolymorphicFunctionObject type that invokes the fusion::reverse() algorithm on its argument. A PolymorphicFunctionObject type that invokes the fusion::reverse() algorithm on its argument. This is useful for defining a CallableTransform like reverse(_), which reverses the order of the children of a Proto expression node. proto::callable This(Expr) fusion::result_of::reverse< typename boost::remove_reference< Expr >::type const > typename fusion::result_of::reverse< Expr const >::type Expr const & Metafunction that computes the return type of proto::flatten() unspecified typename proto::result_of::flatten< Expr const >::type Expr const & A function that returns a "flattened" view of a Proto expression tree. For a tree with a top-most node tag of type T, the elements of the flattened sequence are determined by recursing into each child node with the same tag type and returning those nodes of different type. So for instance, the Proto expression tree corresponding to the expression a | b | c has a flattened view with elements [a, b, c], even though the tree is grouped as ((a | b) | c).