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3.18 Void and Undefined

The constant #<void> is returned by most forms and procedures that have a side-effect and no useful result. The constant #<undefined> is used as the initial value for letrec bindings.

(void? v)  void?
  v : any/c
Returns #t if v is the constant #<void>, #f otherwise.

(void v ...)  void?
  v : any/c
Returns the constant #<void>. Each v argument is ignored.