Generic representations of tree transformations

Abstract

Applications which deal with editing of structured data over multiple iterations, such as structure editors, exercise assistants, or applications which support incremental computation, need to represent transformations between different versions of data. A general notion of "transformation" should be more informative than what is obtained by computing the difference between the old and the new term, as diff algorithms generally consider only insert, copy, and delete operations. Transformations, however, may involve swapping elements, or duplicating them, and a good representation of transformations should not involve unnecessary repetition of data, or lose shared structure between the old and new term.In this paper we take a detailed look at the notion of transformation on strongly-typed structures. Our transformations are datatype-generic, and thus can be applied to a large class of data structures. We focus on representing transformations in a way that maximally captures the common substructure between the old and new term. This is of particular importance to a specific class of applications: that of incremental computations which recompute information only for the parts of the tree that are affected by a transformation.We present three different approaches to the problem, of varying complexity, flexibility, and user-friendliness; different approaches might be better suited for one particular application area or another. We provide practical examples of how to encode transformations in each of the approaches, as well as suggestions on how to apply our solution to larger applications. All approaches use the same underlying generic programming library, and support transformations over families of mutually recursive datatypes.

Incremental Evaluation of Higher Order Attributes

“…In this section we describe how to represent these changes, which is described in (Bransen and Magalhães 2013) in more detail. The representation that we describe here is not only used as an external value to alter the original AST, but also inside the evaluation to keep track of changes to constructed values, as described in Section 6.…”

Lazy stateless incremental evaluation machinery for attribute grammars

“…The approaches based on function caching retain their incremental behaviour in such case, but for approaches like ours an explicit representation of the changes to the AST is needed. To find such a representation we use the diff algorithm from (Bransen and Magalhães 2013).…”

“…Our approach supports all such operations by using the explicit representation of changes from (Bransen and Magalhães 2013).…”

“…For example, a path could select the second child of an Abs node, which only has a single child. These values are intended to be generated only, that is, not hand-written by a human programmer, for example by the algorithm from (Bransen and Magalhães 2013). In this paper we therefore assume that all our edit operations apply to the AST under consideration.…”