message: das.cli: Consume positional arguments and replace them by nothing.
diff: #include <elle/find.hh>
  #include <elle/log.hh>
  #include <elle/make-vector.hh>
  +#include <elle/range.hh>
  #include <elle/serialization/json.hh>
  #include <elle/das/named.hh>
  @@ -452,9 +453,11 @@ namespace elle
  {
  if (this->_positional)
  {
  + ELLE_DEBUG("looking for positional arguments");
  auto it = this->_args.begin();
  while (it != this->_args.end())
  {
  + ELLE_DUMP("evaluating %s", *it);
  // Skip option and possible argument.
  if (is_option(*it))
  {
  @@ -510,7 +513,21 @@ namespace elle
  ELLE_TRACE_SCOPE(
  "convert %s to %s", this->_option, elle::type_info(std::vector<T>{}));
  if (this->_values.empty() && this->_positional)
  - this->_values = std::move(this->_args);
  + {
  + // Take the first contiguous sequence of arguments.
  + auto const begin = boost::find_if(this->_args,
  + [] (auto const& a)
  + {
  + return a != nothing();
  + });
  + auto const end = std::find(begin, this->_args.end(), nothing());
  + this->_values.insert(
  + std::end(this->_values),
  + std::make_move_iterator(begin),
  + std::make_move_iterator(end));
  + for (auto& s: as_range(begin, end))
  + s = nothing();
  + }
  this->_check_remaining();
  return elle::make_vector(this->_values,
  [&] (std::string const& v)
  