- (define-object-type CHILD child? make-child ((parent parent?) (z z? ...) ...) (override ((A a ...) apr ...) ...) ((X (x x? ...) ...) xpr ...) ....)syntax
exports a constructor, (make-child parent z ...), a predicate, child?, as well as messages (X x ...) ... with body xpr ..., whose arguments x are checked by preconditions x? ...
The constructor's argunemts are checked by parent? and z? ... respectively.
In the override clause signatures (A a ...) and overridden bodies apr apr ... of messages already exported and argment-checked by a parent are given.