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4.2.9 Case-lambda

library syntax: case-lambda ⟨clause⟩… ¶

Syntax: Each ⟨clause⟩ is of the form (⟨formals⟩ ⟨body⟩), where ⟨formals⟩ and ⟨body⟩ have the same syntax as in a lambda expression.

Semantics: A case-lambda expression evaluates to a procedure that accepts a variable number of arguments and is lexically scoped in the same manner as a procedure resulting from a lambda expression. When the procedure is called, the first ⟨clause⟩ for which the arguments agree with ⟨formals⟩ is selected, where agreement is specified as for the ⟨formals⟩ of a lambda expression. The variables of ⟨formals⟩ are bound to fresh locations, the values of the arguments are stored in those locations, the ⟨body⟩ is evaluated in the extended environment, and the results of ⟨body⟩ are returned as the results of the procedure call.

It is an error for the arguments not to agree with the ⟨formals⟩ of any ⟨clause⟩.

(define range
  (case-lambda
   ((e) (range 0 e))
   ((b e) (do ((r '() (cons e r))
               (e (- e 1) (- e 1)))
              ((< e b) r)))))

(range 3)    ⇒ (0 1 2)
(range 3 5)  ⇒ (3 4)