Includes Proto callable ``boost::proto::functional::pop_front``.

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(Seq)
result< This(Seq const &) >
This(Seq &)
fusion::result_of::pop_front< Seq >
typename fusion::result_of::pop_front< Seq >::type `Seq &`

`fusion::pop_front(seq)`

typename fusion::result_of::pop_front< Seq const >::type `Seq const &`

`fusion::pop_front(seq)`