(is? ob class)
  ob: any type
  class: any type
  returns a bool

Returns #t if an object or RData belongs to the specified class.

For an object, its class is identified using a reference to a class object. For an RData, its RClass (if any) is identified using a symbol.

(is? obj Rect)
(is? rdata 'Sprite)

The arguments to is? may belong to any type. If the types are other than those noted above, the function will succeed and return #f.