Polytypic programming and data abstraction are important concepts in designing functional programs, but they do not fit well together. Polytypic programming currently depends on making public a free data type representation, while data abstraction depends on hiding the representation. This paper proposes the bialgebra views mechanism as a means of reconciling this conflict. Bialgebra views enable the specification of type structure according to interfaces, not representations, thus combining the genericity of polytypic programming with the information hiding of data abstraction, and narrowing the gap between generic programming in the functional and object-oriented paradigms. Categories and Subject Descriptors D.1.1 [Language Classifications]: