# Pastebin PxfgDP5C
Ah, I didn't see your example until after I had implemented this: sub MAIN() {
    my $repo = CompUnit::RepositoryRegistry.repository-for-name("core");

    my %path-lookup = CORE-LIBRARIES.map: -> $library {
        my $library-dist = $repo.candidates($library).head;
        $library => [ ~ ((try $repo.prefix.add("/sources").add($library-dist.meta<source>)) // "") ]
    }

    say to-json
    %(
        pathLookup => %( |%path-lookup.grep({ so .value.head }) ),
        notInstalled => %path-lookup.grep({ not so .value.head }).map({ .key })
    );
}