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22.7.2.6 Alist Example

Here is a longer example of how alists may be used in practice.

     (define capitals '(("New York" . "Albany")
                        ("Oregon"   . "Salem")
                        ("Florida"  . "Miami")))
     
     ;; What's the capital of Oregon?
     (assoc "Oregon" capitals)       ⇒ ("Oregon" . "Salem")
     (assoc-ref capitals "Oregon")   ⇒ "Salem"
     
     ;; We left out South Dakota.
     (set! capitals
           (assoc-set! capitals "South Dakota" "Pierre"))
     capitals
     ⇒
     (("South Dakota" . "Pierre")
      ("New York" . "Albany")
      ("Oregon" . "Salem")
      ("Florida" . "Miami"))
     
     ;; And we got Florida wrong.
     (set! capitals
           (assoc-set! capitals "Florida" "Tallahassee"))
     capitals
     ⇒
     (("South Dakota" . "Pierre")
      ("New York" . "Albany")
      ("Oregon" . "Salem")
      ("Florida" . "Tallahassee"))
     
     ;; After Oregon secedes, we can remove it.
     (set! capitals
           (assoc-remove! capitals "Oregon"))
     capitals
     ⇒
     (("South Dakota" . "Pierre")
      ("New York" . "Albany")
      ("Florida" . "Tallahassee"))