[rwl]

My point is not that this is impossible; it's that separating the tasks of building a list of query results and then executing an operation on those results requires some kind of convention about how to refer to those results across the two phases. Developing such a convention is a harder problem than it looks like.

The example I was responding to was from the (Unix) shell, which as far as I am aware does not offer any such convention other than filenames. Real programming languages of course offer more options, but even there the problem is not solved: as you say, you must then build the system which understands how to take the results of the query and execute something on them. That means designing such a convention inside your program. The article is about using a type system to help you do that cleanly.