Testing properties of generic functions

A datatype-generic function is a family of functions indexed by (the structure of) a type. Examples include equality tests, maps and pretty printers. Property based testing tools like QuickCheck and Gast support the de¯nition of properties and test-data generators, and they check if a monomorphic property is satis¯ed by the test cases. Generic functions satisfy generic properties and this paper discusses specifying and testing such properties. It shows how generic properties and gener- ators can be expressed, and explains three bugs we found and corrected in the Generic Haskell librar