Boomerang

Abstract

A lens is a bidirectional program. When read from left to right, it denotes an ordinary function that maps inputs to outputs. When read from right to left, it denotes an "update translator" that takes an input together with an updated output and produces a new input that reflects the update. Many variants of this idea have been explored in the literature, but none deal fully with ordered data. If, for example, an update changes the order of a list in the output, the items in the output list and the chunks of the input that generated them can be misaligned, leading to lost or corrupted data.We attack this problem in the context of bidirectional transformations over strings, the primordial ordered data type. We first propose a collection of bidirectional string lens combinators, based on familiar operations on regular transducers (union, concatenation, Kleene-star) and with a type system based on regular expressions. We then design a new semantic space of dictionary lenses, enriching the lenses of Foster et al. (2007b) with support for two additional combinators for marking "reorderable chunks" and their keys. To demonstrate the effectiveness of these primitives, we describe the design and implementation of Boomerang, a full-blown bidirectional programming language with dictionary lenses at its core. We have used Boomerang to build transformers for complex real-world data formats including the SwissProt genomic database.We formalize the essential property of resourcefulness-the correct use of keys to associate chunks in the input and output-by defining a refined semantic space of quasi-oblivious lenses. Several previously studied properties of lenses turn out to have compact characterizations in this space.(the default year range 0000-0000 is generated by the del lens in comp from the regular expression YEARS). Problems with OrderOn other examples, however, the behavior of this put function is highly unsatisfactory. If the update to the abstract string breaks the positional association between lines in the concrete and abstract strings, the output will be mangled-e.g., when the update to the abstract string is a reordering, combining

Narcissus: correct-by-construction derivation of decoders and encoders from binary formats

“…Narcissus has a similar motivation to bidirectional programming languages [Bohannon et al 2008;Mu et al 2004] in which programs can be run łin reversež to map target values to the source values that produced them. The bidirectional programming language Boomerang adopts a similar combinator-based approach to deriving transformations between target and source values.…”

“…Boomerang [Bohannon et al 2008] is a bidirectional programming language for projecting transformations on a data view back to the original source data; in contrast to Narcissus, Boomerang does not require that the original source values can be recovered from a target view. Boomerang programs are built using a collection of lens combinators, which include get, put, and create operations for transporting modifications between source and target representations.…”

End To End Development Engineering

“…Synchronization tools are normally built on some underlying algebraic theory [28,53,40,5,2,41,30], and many such tools (the first five amongst those cited above) use algebraic theories based on state-based rather than delta-based operations. The state-based version of the propagation scenario in Fig.…”

Category Theory and Model-Driven Engineering: From Formal Semantics to Design Patterns and Beyond

“…As mentioned above, understanding the semantics of model synchronization procedures is important, both theoretically and practically. Synchronization tools are normally built on some underlying algebraic theory [28,53,40,4,1,41,30], and many such tools (the first five amongst those cited above) use algebraic theories based on state-based rather than delta-based operations. The state-based version of the propagation scenario in Fig.…”