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2.13 Dispatch: case

(case val-expr case-clause ...)
case-clause = [(datum ...) then-body ...+]
  | [else then-body ...+]
Evaluates val-expr and uses the result to select a case-clause. The selected clause is the first one with a datum whose quoted form is eqv? to the result of val-expr. If no such datum is present, the else case-clause is selected; if no else case-clause is present, either, then the result of the case form is #<void>.

For the selected case-clause, the results of the last then-body, which is in tail position with respect to the case form, are the results for the whole case form.

A case-clause that starts with else must be the last case-clause.


  > (case (+ 7 5)
     [(1 2 3) 'small]
     [(10 11 12) 'big])


  > (case (- 7 5)
     [(1 2 3) 'small]
     [(10 11 12) 'big])


  (define (classify c)
    (case (char-general-category c)
     [(ll lu lt ln lo) "letter"]
     [(nd nl no) "number"]
     [else "other"]))


  > (classify #\A)


  > (classify #\1)


  > (classify #\!)