Type-Directed Di ng of Structured Data

Abstract The Unix diff utility that compares lines of text is used pervasively by version control systems. Yet certain changes to a program may be di cult to describe accurately in terms of modi cations to individual lines of code. As a result, observing changes at such a xed granularity may lead to unnecessary con icts between di erent edits. This paper presents a generic representation for describing transformations between algebraic data types and a non-deterministic algorithm for computing such representations. These representations can be used to give a more accurate account of modi cations made to algebraic data structures – and the abstract syntax trees of computer programs in particular – as opposed to only considering modi cations between their textual representations. CCS Concepts •Software and its engineering→ Functional languages; Data types and structures; •Applied computing → Version control;