Problem 2.   A package company keeps track of three kinds of packages: regular, express, and overnight. The company uses three different classes of data to represent the relevant information:

  (define-struct regular (zip))
  (define-struct express (zip zap zoom))
  (define-struct overnight (zip zap))

  ;; A Package is one of: 
  ;; -- (make-regular TenNumber)
  ;; -- (make-express TenNumber Symbol Number)
  ;; -- (make-overnight TenNumber Symbol)

  ;; A TenNumber is a Number between 1 and 9999 (inclusive). 

This problem consists of three, independent parts. In order to solve one part, you do not need to know the solution for any other part.

• Name the constructor, selectors, and predicate that the structure definition for regular introduces.

  Solution:

  make-regular regular-zip regular? ; [PT 1, for all]
  

• Make up three examples for Packages, one from each subclass.

  Solution:

  ;[PT 3, one each]
  (make-regular 890)
  (make-express 9999 'High -10)
  (make-overnight 1 'Low)
  

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