Abstract
Spreadsheets play a pivotal role in many organizations. They serve to store and manipulate data or forecasting, and they are often used to help in the decision process, thus directly impacting the success, or not, of organizations. As the research community already realized, spreadsheets tend to have the same problems “professional” software contain. Thus, in the past decade many software engineering techniques have been successfully proposed to aid spreadsheet developers and users. However, one of the most used mechanisms to manage software projects is still lacking in spreadsheets: a version control system. A version control system allows for collaborative development, while also allowing individual developers to explore different alternatives without compromising the main project. In this paper we present a version control system, named SheetGit, oriented for end-user programmers. It allows to graphically visualize the history of versions (including branches), to switch between different versions just by pointing and clicking, and to visualize the differences between any two versions in an animated way. To validate our approach/tool we performed an empirical evaluation which shows evidence that SheetGit can aid users when compared to other tools.

Abstract
To infer an abstract model from source code is one of the main tasks of most software quality analysis methods. Such abstract model is called Abstract Syntax Tree and the inference task is called parsing. A parser is usually generated from a grammar specification of a (programming) language and it converts source code of that language into said abstract tree representation. Then, several techniques traverse this tree to assess the quality of the code (for example by computing source code metrics), or by building new data structures (e.g, flow graphs) to perform further analysis (such as, code cloning, dead code, etc). Parsing is a well established technique. In recent years, however, modern languages are inherently ambiguous which can only be fully handled by ambiguous grammars. In this setting disambiguation rules, which are usually included as part of the grammar specification of the ambiguous language, need to be defined. This approach has a severe limitation: disambiguation rules are not first class citizens. Parser generators offer a small set of rules that can not be extended or changed. Thus, grammar writers are not able to manipulate nor define a new specific rule that the language he is considering requires. In this paper we present a tool, name InDubio, that consists of an extensible combinator library of disambiguation filters together with a generalized parser generator for ambiguous grammars. InDubio defines a set of basic disambiguation rules as abstract syntax tree filters that can be combined into more powerful rules. Moreover, the filters are independent of the parser generator and parsing technology, and consequently, they can be easily extended and manipulated. This paper presents InDubio in detail and also presents our first experimental results.

Abstract
Software testing is an integral part of modern software development. Testing frameworks are part of the toolset of any software language allowing programmers to test their programs in order to detect bugs. Unfortunately, there is no work on testing in attribute grammars. In this paper we combine the powerful property-based testing technique with the attribute grammar formalism. In such property-based attribute grammars, properties are defined on attribute instances. Properties are tested on large sets of randomly generated (abstract syntax) trees by evaluating their attributes. We present an implementation that relies on strategies to express property-based attribute grammars. Strategies are tree-based recursion patterns that are used to encode logic quantifiers defining the properties.

Abstract
Contrarily to most conventional programming languages where certain symbols are used so as to create non-ambiguous grammars, most recent programming languages allow ambiguity. These ambiguities are solved using disambiguation rules, which dictate how the software that parses these languages should behave when faced with ambiguities. Such rules are highly efficient but come with some limitations - they cannot be further modified, their behaviour is hidden, and changing them implies re-building a parser. We propose a different approach for disambiguation. A set of disambiguation filters (expressed as combinators) are provided, and disambiguation can be achieved by composing combinators. New combinators can be created and, by having the disambiguation step separated from the parsing step, disambiguation rules can be changed without modifying the parser.

Abstract
This paper presents pyZtrategic: a library that embeds strategic term rewriting and attribute grammars in the Python programming language. Strategic term rewriting and attribute grammars are two powerful programming techniques widely used in language engineering: The former relies on strategies to apply term rewrite rules in defining large-scale language transformations, while the latter is suitable to express context-dependent language processing algorithms. Thus, pyZtrategic offers Python programmers recursion schemes (strategies) which apply term rewrite rules in defining large scale language transformations. It also offers attribute grammars to express context-dependent language processing algorithms. PyZtrategic offers the best of those two worlds, thus providing powerful abstractions to express software maintenance and evolution tasks. Moreover, we developed several language engineering problems in pyZtrategic, and we compare it to well established strategic programming and attribute grammar systems. Our preliminary results show that our library offers similar expressiveness as such systems, but, unfortunately, it does suffer from the current poor runtime performance of the Python language.

Abstract
Strategic term re-writing and attribute grammars are two powerful programming techniques widely used in language engineering. The former relies on strategies to apply term re-write rules in defining largescale language transformations, while the latter is suitable to express context-dependent language processing algorithms. These two techniques can be expressed and combined via a powerful navigation abstraction: generic zippers. This results in a concise zipper-based embedding offering the expressiveness of both techniques. In addition, we increase the functionalities of strategic programming, enabling the definition of outwards traversals; i.e. outside the starting position. Such elegant embedding has a severe limitation since it recomputes attribute values. This paper presents a proper and efficient embedding of both techniques. First, attribute values are memoized in the zipper data structure, thus avoiding their re-computation. Moreover, strategic zipper based functions are adapted to access such memoized values. We have hosted our memoized zipper-based embedding of strategic attribute grammars both in the Haskell and Python programming languages. Moreover, we benchmarked the libraries supporting both embedding against the state-of-the-art Haskell-based Strafunski and Scala-based Kiama libraries. The first results show that our Haskell Ztrategic library is very competitive against those two well established libraries.