Object-Oriented Programming (OOP) is a method of data abstraction that allows one to write flexible programs that are independent of the implementation of the data on which they operate.
Consider ways of implementing vectors:
If we write a program that obtains the x value from a vector v by doing (car v), that program will work for some kinds of vectors but not for others.
If, instead, we use a message (send v 'x), then our program can work for all the kinds of vectors (even new ones to be added later).
(define (vector-x self) (cadr self))
(define (polar-x self) (* (cadr self) (cos (caddr self))) )
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