Abstract

Polymorphic regular types are tree-like datatypes generated by polynomial type expressions over a set of free variables and closed under least fixed point. The ‘equality types ’ of Core ML can be expressed in this form. Given such a type expression with free, this paper shows a way to represent the one-hole contexts for elements of within elements of, together with an operation which will plug an element of into the hole of such a context. One-hole contexts are given as inhabitants of a regular type, computed generically from the syntactic structure of by a mechanism better known as partial differentiation. The relevant notion of containment is shown to be appropriately characterized in terms of derivatives and plugging in. The technology is then exploited to give the one-hole contexts for sub-elements of recursive types in a manner similar to Huet’s ‘zippers’[Hue97]. 1

Citations

161	PolyP—A polytypic programming language extension - Jansson, Jeuring - 1997
71	The zipper - Huet - 1997
71	Foncteurs analytiques et esp`eces de structures - Joyal - 1986
70	Inductive sets and families in Martin-Lof’s type theory and their set-theoretic semantics - Dybjer - 1991
67	Nested datatypes - Bird, Meertens - 1998
62	De Bruijn notation as a nested datatype - Bird, Paterson - 1999
61	Dependently Typed Functional Programs and Their Proofs - McBride - 2000
8	Generic Programming—An Introduction - Backhouse, Jansson, et al. - 1998
4	Computer Aided Manipulation of Symbols - McBride - 1970