Technical Reports (CIS)

Document Type

Technical Report

Date of this Version

January 2009

Comments

University of Pennsylvania Department of Computer and Information Science Technical Report No. MS-CIS-09-06

Abstract

Binding is a fundamental part of language specification, yet it is both difficult and tedious to get right. In previous work, we argued that an approach based on locally nameless representation and a particular style for defining inductive relations can provide a portable, transparent, lightweight methodology to define the semantics of binding. Although the binding infrastructure required by this approach is straightforward to develop, it leads to duplicated effort and code as the number of binding forms in a language increases.

In this paper, we critically compare a spectrum of approaches that attempt to ameliorate this tedium by unifying the treatment of variables and binding. In particular, we compare our original methodology with two alternative ideas: First, we define variable binding in the object language via variable binding in a reusable library. Second, we present a novel approach that collapses the syntactic categories of the object language together, permitting variables to be shared between them.

Our main contribution is a careful characterization of the benefits and drawbacks of each approach. In particular, we use multiple solutions to the POPLMARK challenge in the Coq proof assistant to point out specic consequences with respect to the size of the binding infrastructure, transparency of the definitions, impact to the metatheory of the object language, and adequacy of the object language encoding.

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Date Posted: 12 March 2009