Pacman UX may be difficult to getting started, however once learn a bit it is really easy. For example, you know the "-S something" install a package named "something" and "-Ss" search a package in repositories. So, how to search an installed package? Well, there is "-Q' parameter that installs a local package, so maybe:

$ pacman -Qs package

And yeah, this is exactly how it works. Once you learn a bit about how pacman works, it all connects, same thing as vim.