Please provide an example for parsing a file

In spirit x3 we could use

```
#include

typedef boost::spirit::istream_iterator iterator_t;

std::ifstream stream(file);
iterator_t iterator(stream);

const bool ok = x3::phrase_parse
(
iterator, iterator_t(),
,
,

);
```

What is your design to do this job in boost::parser now?
The solution should be part of the documentation.

Thanks!