For example, the query
(who is the director of the godfather)
matches the pattern
(who is the director of ...)
When a pattern is matched, an associated
action is taken, namely, run a procedure.
For our example, the procedure to run is
(lambda (title)
(movies-satisfying
our-movie-database
(lambda (movie)
(equal? (movie-title movie) title))
movie-director))
on the argument
(the godfather).