Bug

The input buffer should be emptied after the first answer

Verify package status (anonymously)
        at "https://www.swi-prolog.org/pack/query" Y/n?

If you type Y+Enter here, the second answer needs no input to proceed

Install "by_unix-0.2.tgz" (15,238 bytes) Y/n?
true.

Problem

As is the custom for Prolog (due to its intended use), this predicate fails if there is a problem leaving you clueless as to what went wrong. We need a general approach for this kind of problem. Like a non-backtrackable rolling log in the Prolog database.

The upgrade option doesn't appear to work:

?- pack_install(pubmed, [upgrade(true)]).
% Contacting server at http://www.swi-prolog.org/pack/query ... ok
% Pack `pubmed' is already installed @0.0.1
true.

This is despite 0.0.4 of pubmed being available

"Use default answer without asking the user if there is a default action."

->

"If false (default is true), use default answer without asking the user if there is a default action."

?