The observation that program structure follows data structure is a key lesson in introductory programming: good hints for possible program designs can be found by considering the structure of the data concerned. In particular, this lesson is a core message of the influential textbook “How to Design Programs” by Felleisen, Findler, Flatt, and Krishnamurthi. However, that book discusses using only the structure of input data for guiding program design, typically leading towards structurally recursive programs. We argue that novice programmers should also be taught to consider the structure of output data, leading them also towards structurally corecursive programs.

I am Professor of Computing in the Department of Computer Science at the University of Oxford. I also lead the Algebra of Programming research group. I have served as Deputy Head of Department, and as Director of the Software Engineering Programme, which offers part-time professional Masters’ degrees in Software Engineering and in Software and Systems Security. I am Editor-in-Chief of the Journal of Functional Programming, Chair of the ICFP Steering Committee, Past Vice Chair of ACM SIGPLAN, Past Chair of IFIP WG2.1. Before taking up this post in 1999, I held lectureships at Oxford Brookes University and the University of Auckland, New Zealand.