CPL is a functional programming language based on category theory. Data types are declared in a categorical manner by adjunctions. Data types that can be handled include the terminal object, the initial object, the binary product functor, the binary coproduct functor, the exponential functor, the natural number object, the functor for finite lists, and the functor for infinite lists. Each data type is declared with its basic operations or morphisms. Programs consist of these morphisms, and execution of programs is the reduction of elements (i.e. special morphisms) to their canonical form.