I'd like to be able to take a resource path that returns multiple results and then apply list operations to them.

It looks like I can get close but not quite, so I'm looking for advice - and potentially a new built-in suited to this case - a resource path version of log:collectAllIn, e.g. log:asList.

It looks like this works, but only because it's counting number of blank nodes for ?x

{?formula ex:asList ?list.} <= {
  ( ?x  ?formula  ?list ) log:collectAllIn _:x .
}.

{
  ?product a schema:Product.
  {?product^sosa:observedProperty}!ex:asList!list:length log:equalTo ?nObs.
}=>
{
  ?product ex:nobs ?nObs.
}.

This then doesn't work, because ?last is just a blank node:

{
  ?product a schema:Product.                                              
  {?product^sosa:observedProperty}!ex:asList!list:last log:equalTo ?last.
}=>
{
  ?product ex:last ?last.
}.

Is there a way to match the result from a resource path so that it can be extracted by log:collectAllIn?