“Explosive” Programming Controlled by Calculation

In the design of a functional library in the area of data-mining several algorithmic patterns have been identified which call for generic programming. Some of these have to do with flattening functions which arise in a particular group of hierarchical systems. In this paper we describe our efforts to make such functionalities generic. We start by a generic inductive construction of the intended class of hierarchical types. We conclude by relating the structure of the relevant base-functors with the algebraic structure which is required by the generic flattening functionality, in particular concerning its “deforestation” towards a linearly complex implementation. The instances we provide as examples include the widely known bill of materials “explode” operation.