Wed 10 Jan 2018 10:30 - 10:55 at Bunker Hill - Strings Chair(s): Zachary Tatlock

Bidirectional transformations between different data representations occur frequently in modern software systems. They appear as serializers and deserializers, as parsers and pretty printers, as database views and view updaters, and as a multitude of different kinds of ad hoc data converters. Manually building bidirectional transformations—by writing two separate functions that are intended to be inverses—is tedious and error prone. A better approach is to use a domain-specific language in which both directions can be written as a single expression. However, these domain-specific languages can be difficult to program in, requiring programmers to manage fiddly details while working in a complex type system.

We present an alternative approach.
Instead of coding transformations manually, we synthesize them from declarative format descriptions and examples. Specifically, we present Optician, a tool for type-directed synthesis of bijective string transformers. The inputs to Optician are a pair of ordinary regular expressions representing two data formats and a few concrete examples for disambiguation. The output is a well-typed program in Boomerang (a bidirectional language based on the theory of lenses). The main technical challenge involves navigating the vast program search space efficiently enough. In particular, and unlike most prior work on type-directed synthesis, our system operates in the context of a language with a rich equivalence relation on types (the theory of regular expressions). Consequently, program synthesis requires search in two dimensions: First, our synthesis algorithm must find a pair of “syntactically compatible types,” and second, using the structure of those types, it must find a type- and example-compliant term. Our key insight is that it is possible to reduce the size of this search space without losing any computational power by defining a new language of lenses designed specifically for synthesis. The new language is free from arbitrary function composition and operates only over types and terms in a new disjunctive normal form. We prove (1) our new language is just as powerful as a more natural, compositional, and declarative language and (2) our synthesis algorithm is sound and complete with respect to the new language. We also demonstrate empirically that our new language changes the synthesis problem from one that admits intractable solutions to one that admits highly efficient solutions, able to synthesize lenses between complex file formats with great variation in seconds.
We evaluate Optician on a benchmark suite of 39 examples that includes both microbenchmarks and realistic examples derived from other data management systems including Flash Fill, a tool for synthesizing string transformations in spreadsheets, and Augeas, a tool for bidirectional processing of Linux system configuration files.

Wed 10 Jan
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10:30 - 12:10: StringsResearch Papers at Bunker Hill
Chair(s): Zachary TatlockUniversity of Washington, Seattle
10:30 - 10:55
Synthesizing Bijective Lenses
Research Papers
Anders MiltnerPrinceton University, Kathleen FisherTufts University, Benjamin C. PierceUniversity of Pennsylvania, David WalkerPrinceton University, Steve ZdancewicUniversity of Pennsylvania
10:55 - 11:20
WebRelate: Integrating Web Data with Spreadsheets using Examples
Research Papers
Jeevana Priya InalaMIT, Rishabh SinghMicrosoft Research
11:20 - 11:45
What's Decidable About String Constraints with ReplaceAll Function?
Research Papers
Taolue ChenBirkbeck, University of London, Yan ChenState Key Laboratory of Computer Science, Institute of Software, Chinese Academy of Sciences & University of Chinese Academy of Sciences, Matthew HagueRoyal Holloway, University of London, Anthony Widjaja LinOxford University, Zhilin WuState Key Laboratory of Computer Science, Institute of Software, Chinese Academy of Sciences
11:45 - 12:10
String Constraints with Concatenation and Transducers Solved Efficiently
Research Papers
Lukáš HolíkBrno University of Technology, Anthony Widjaja LinOxford University, Petr JankůBrno University of Technology, Philipp RuemmerUppsala University, Tomáš VojnarBrno University of Technology