Objects and Subtyping in a Functional Perspective

IBM Research Report RC 16423, March 1991

Martin Odersky 

Object-oriented programming languages with subtyping facilitate the
reuse of code which forms the top part of a call graph. This style of
code reuse, sometimes called inverted programming, cannot be simulated
easily in traditional languages.  We present a technique for achieving
the same effect in the framework of a higher-order, polymorphic
functional language without subtyping. Our method establishes a close
relationship between the object-oriented concepts of class, ``self'',
and subtyping, and the functional concepts of algebraic data types and
abstraction functions. This relationship can form the basis of a
transformational semantics of object-oriented language elements.