Syntactic Sugar Research Articles

Semantics Lifting for Syntactic Sugar

Syntactic sugar plays a crucial role in engineering programming languages. It offers convenient syntax and higher-level of abstractions, as witnessed by its pervasive use in both general-purpose and domain-specific contexts. Unfortunately, the traditional approach of translating programs containing syntactic sugars into the host language can lead to abstraction leakage, breaking the promise of convenience and hindering program comprehension. To address this challenge, we introduce the idea of semantics lifting that aims to statically derive self-contained evaluation rules for syntactic sugars. More specifically, we propose a semantics-lifting framework that consists of (i) a general algorithm for deriving host-independent semantics of syntactic sugars from the semantics of the host language and the desugaring rules, (ii) a formulation of the correctness and abstraction properties for a lifted semantics, and (iii) a systematic investigation of sufficient conditions that ensure a lifted semantics is provably correct and abstract. To evaluate our semantics-lifting framework, we have implemented a system named Osazone and conducted several case studies, demonstrating that our approach is flexible, effective, and practical for implementing domain-specific languages.

An efficient algorithm for reasoning over OWL EL ontologies with nominal schemas

Abstract Nominal schemas have been proposed as an extension to Description Logics (DL), the knowledge representation paradigm underlying the Web Ontology Language (OWL). They provide for a very tight integration of DL and rules. Nominal schemas can be understood as syntactic sugar on top of OWL. However, this naive perspective leads to inefficient reasoning procedures. In order to develop an efficient reasoning procedure for the language ${\mathcal {E}\mathcal {L}\mathcal {V}^{++}}$, which results from extending the OWL profile language OWL EL with nominal schemas, we propose a transformation from ${\mathcal {E}\mathcal {L}\mathcal {V}^{++}}$ ontologies into Datalog-like rule programs that can be used for satisfiability checking and assertion retrieval. The use of this transformation enables the use of powerful Datalog engines to solve reasoning tasks over ${\mathcal {E}\mathcal {L}\mathcal {V}^{++}}$ ontologies. We implement and then evaluate our approach on several real-world, data-intensive ontologies, and find that it can outperform state-of-the-art reasoners such as Konclude and ELK. As a lesser side result we also provide a self-contained description of a rule-based algorithm for ${\mathcal {E}\mathcal {L}^{++}}$, which does not require a normal form transformation.

Beyond Notations: Hygienic Macro Expansion for Theorem Proving Languages

In interactive theorem provers (ITPs), extensible syntax is not only crucial to lower the cognitive burden of manipulating complex mathematical objects, but plays a critical role in developing reusable abstractions in libraries. Most ITPs support such extensions in the form of restrictive "syntax sugar" substitutions and other ad hoc mechanisms, which are too rudimentary to support many desirable abstractions. As a result, libraries are littered with unnecessary redundancy. Tactic languages in these systems are plagued by a seemingly unrelated issue: accidental name capture, which often produces unexpected and counterintuitive behavior. We take ideas from the Scheme family of programming languages and solve these two problems simultaneously by proposing a novel hygienic macro system custom-built for ITPs. We further describe how our approach can be extended to cover type-directed macro expansion resulting in a single, uniform system offering multiple abstraction levels that range from supporting simplest syntax sugars to elaboration of formerly baked-in syntax. We have implemented our new macro system and integrated it into the new version of the Lean theorem prover, Lean 4. Despite its expressivity, the macro system is simple enough that it can easily be integrated into other systems.

Logical English meets legal English for swaps and derivatives

In this paper, we present an informal introduction to Logical English (LE) and illustrate its use to standardise the legal wording of the Automatic Early Termination (AET) clauses of International Swaps and Derivatives Association (ISDA) Agreements. LE can be viewed both as an alternative to conventional legal English for expressing legal documents, and as an alternative to conventional computer languages for automating legal documents. LE is a controlled natural language (CNL), which is designed both to be computer-executable and to be readable by English speakers without special training. The basic form of LE is syntactic sugar for logic programs, in which all sentences have the same standard form, either as rules of the form conclusion if conditions or as unconditional sentences of the form conclusion. However, LE extends normal logic programming by introducing features that are present in other computer languages and other logics. These features include typed variables signalled by common nouns, and existentially quantified variables in the conclusions of sentences signalled by indefinite articles. Although LE translates naturally into a logic programming language such as Prolog or ASP, it can also serve as a neutral standard, which can be compiled into other lower-level computer languages.

Digitizing Service Level Agreements in Service-Oriented Enterprise Architecture

As service-orientation gathers traction in enterprise engineering, more and more business processes and capabilities alike are wrapped up and viewed as services in today’s digital enterprises. Digital servitization is neither a rebranding nor a syntax sugar in enterprise engineering. It opens the door to innovative business models, novel system architecture, to name just a few. Central to service provisioning is the notion of commitment that captures contractual agreements between the provider and the consumer of the service in question, describing not only computer-interpretable factors (e.g., reliability, payment), but also business rules (e.g., service penalty) of the commitment. Widely known as the service level agreement, this building block of service-oriented enterprise engineering is pushed towards virtual when it comes to digital servitization. In this article, we propose a descriptive framework for digital enterprise services together with devised techniques for the alignment and reinforcement of the service level agreement. The relevance and applicability of the multi-perspective approach to service engineering are among our findings, which are illustrated using a few examples and a real-life case-study.

Unifying Parsing and Reflective Printing for Fully Disambiguated Grammars

Language designers usually need to implement parsers and printers. Despite being two closely related programs, in practice they are often designed separately, and then need to be revised and kept consistent as the language evolves. It will be more convenient if the parser and printer can be unified and developed in a single program, with their consistency guaranteed automatically. Furthermore, in certain scenarios (like showing compiler optimisation results to the programmer), it is desirable to have a more powerful reflective printer that, when an abstract syntax tree corresponding to a piece of program text is modified, can propagate the modification to the program text while preserving layouts, comments, and syntactic sugar. To address these needs, we propose a domain-specific language BiYacc, whose programs denote both a parser and a reflective printer for a fully disambiguated context-free grammar. BiYacc is based on the theory of bidirectional transformations, which helps to guarantee by construction that the generated pairs of parsers and reflective printers are consistent. Handling grammatical ambiguity is particularly challenging: we propose an approach based on generalised parsing and disambiguation filters, which produce all the parse results and (try to) select the only correct one in the parsing direction; the filters are carefully bidirectionalised so that they also work in the printing direction and do not break the consistency between the parsers and reflective printers. We show that BiYacc is capable of facilitating many tasks such as Pombrio and Krishnamurthi’s ‘resugaring’, simple refactoring, and language evolution.

Tapir

Tapir (pronounced TAY-per) is a compiler intermediate representation (IR) that embeds recursive fork-join parallelism, as supported by task-parallel programming platforms such as Cilk and OpenMP, into a mainstream compiler’s IR. Mainstream compilers typically treat parallel linguistic constructs as syntactic sugar for function calls into a parallel runtime. These calls prevent the compiler from performing optimizations on and across parallel control constructs. Remedying this situation has generally been thought to require an extensive reworking of compiler analyses and code transformations to handle parallel semantics. Tapir leverages the “serial-projection property,” which is commonly satisfied by task-parallel programs, to handle the semantics of these programs without an extensive rework of the compiler. For recursive fork-join programs that satisfy the serial-projection property, Tapir enables effective compiler optimization of parallel programs with only minor changes to existing compiler analyses and code transformations. Tapir uses the serial-projection property to order logically parallel fine-grained tasks in the program’s control-flow graph. This ordered representation of parallel tasks allows the compiler to optimize parallel codes effectively with only minor modifications. For example, to implement Tapir/LLVM, a prototype of Tapir in the LLVM compiler, we added or modified less than 3,000 lines of LLVM’s half-million-line core middle-end functionality. These changes sufficed to enable LLVM’s existing compiler optimizations for serial code—including loop-invariant-code motion, common-subexpression elimination, and tail-recursion elimination—to work with parallel control constructs such as parallel loops and Cilk’s Cilk_Spawn keyword. Tapir also supports parallel optimizations, such as loop scheduling, which restructure the parallel control flow of the program. By making use of existing LLVM optimizations and new parallel optimizations, Tapir/LLVM can optimize recursive fork-join programs more effectively than traditional compilation methods. On a suite of 35 Cilk application benchmarks, Tapir/LLVM produces more efficient executables for 30 benchmarks, with faster 18-core running times for 26 of them, compared to a nearly identical compiler that compiles parallel linguistic constructs the traditional way.

Generic Programming in OCaml

We present a library for generic programming in OCaml, adapting some techniques borrowed from other functional languages. The library makes use of three recent additions to OCaml: generalised abstract datatypes are essential to reflect types, extensible variants allow this reflection to be open for new additions, and extension points provide syntactic sugar and generate boiler plate code that simplify the use of the library. The building blocks of the library can be used to support many approaches to generic programming through the concept of view. Generic traversals are implemented on top of the library and provide powerful combinators to write concise definitions of recursive functions over complex tree types. Our case study is a type-safe deserialisation function that respects type abstraction.

Implementing HTTP-Service in a Functional Domain-Specific Language Based on Free Monads

Implementing web-services in a pure functional way is not a trivial task, because it is common to a query database (or a different type of mutable data store) on all the stages of the server request processing. This complicates separation of the pure functional core and imperative shell of the program, which is the primary principle of the functional software architecture. This article focuses on resolving this problem by using free monads, which makes it possible to implement a new domain-specific language that is defined by purely functional data structures, to describe imperative operations. Each operation is later interpreted into actual data mutation by an interpreter. This allows defining the algorithms as a combination of atomic DSL operations, which may have side-effects, in a purely functional way, while only the interpretation logic of those operations remains imperative.In contrast to a standard approach, the amount of the imperative code in free monad based algorithms scales depending on the number of atomic DSL operations instead of the size of the whole program. This can bring a big difference, especially if atomic operations are frequently re-used. As part of the research, an HTTP-based message exchange service was implemented in its own free monad based domain-specific language. As a basis, functional programming language Scala was used. The article shows the implementation of the server endpoint that sends the message to a specific conversation. The endpoint implementation consists of many atomic database queries and contains multiple branches of the control flow.First, each atomic database query or group of related queries is described as a pure functional record where dynamic query parameters are defined as values of the record fields. Then, using a free monad constructor, these operators are upgraded to monads and get the combination logic from the already existing monadic instances. Usually either one is used as a basis, since it provides a convenient way to handle exceptions. Next, atomic monadic operations are combined into algorithms. Most functional languages have syntactic sugar to write expressions, which combine multiple monads. In case of Scala, it is a for-expression. To interpret a DSL-based expression, an interpreter should be declared and used. The interpreter is a function with a defined behaviour for atomic DSL operations which are defined earlier. This behaviour may not be purely functional and may have side effects.The conducted research confirms that the usage of free monad based functional domain-specific programming languages is suitable in context of implementing HTTP-services, and it may significantly decrease the amount of the imperative code.

Compiler Front End Fusion: Undo Desugaring in Language Processing Tools

Compiler front ends often perform desugaring on the source code while constructing the abstract syntax tree (AST). A programming language processing tool (such as a refactoring tool) working with the desugared AST perceives the code at this abstract level, and loses information on the rich syntax used in the actual source code. This paper discusses the concept of front end fusion, a technique which may help language processing tools to retain the syntactic sugar information on the source code in the presence of desugaring compiler front ends. We propose a hybrid front end created from two separate front ends: one provided by the compiler, which offers type information, and another one, which provides the details of the concrete syntax used in the source code. Specifically, we show how to construct a hybrid front end in a language processing tool for the Scala programming language.

Inferring type rules for syntactic sugar

Type systems and syntactic sugar are both valuable to programmers, but sometimes at odds. While sugar is a valuable mechanism for implementing realistic languages, the expansion process obscures program source structure. As a result, type errors can reference terms the programmers did not write (and even constructs they do not know), baffling them. The language developer must also manually construct type rules for the sugars, to give a typed account of the surface language. We address these problems by presenting a process for automatically reconstructing type rules for the surface language using rules for the core. We have implemented this theory, and show several interesting case studies.

Inferring scope through syntactic sugar

Many languages use syntactic sugar to define parts of their surface language in terms of a smaller core. Thus some properties of the surface language, like its scoping rules , are not immediately evident. Nevertheless, IDEs, refactorers, and other tools that traffic in source code depend on these rules to present information to users and to soundly perform their operations. In this paper, we show how to lift scoping rules defined on a core language to rules on the surface, a process of scope inference . In the process we introduce a new representation of binding structure---scope as a preorder---and present a theoretical advance: proving that a desugaring system preserves α-equivalence even though scoping rules have been provided only for the core language. We have also implemented the system presented in this paper.

Tapir

This paper explores how fork-join parallelism, as supported by concurrency platforms such as Cilk and OpenMP, can be embedded into a compiler's intermediate representation (IR). Mainstream compilers typically treat parallel linguistic constructs as syntactic sugar for function calls into a parallel runtime. These calls prevent the compiler from performing optimizations across parallel control constructs. Remedying this situation is generally thought to require an extensive reworking of compiler analyses and code transformations to handle parallel semantics. Tapir is a compiler IR that represents logically parallel tasks asymmetrically in the program's control flow graph. Tapir allows the compiler to optimize across parallel control constructs with only minor changes to its existing analyses and code transformations. To prototype Tapir in the LLVM compiler, for example, we added or modified about 6000 lines of LLVM's 4-million-line codebase. Tapir enables LLVM's existing compiler optimizations for serial code -- including loop-invariant-code motion, common-subexpression elimination, and tail-recursion elimination -- to work with parallel control constructs such as spawning and parallel loops. Tapir also supports parallel optimizations such as loop scheduling.

Hierarchical and Concurrent ECCs for IEC 61499 Function Blocks

IEC 61499 enables component-oriented descriptions of complex industrial processes facilitating model-driven engineering. One aspect that is lacking, however, is the ability to directly express Statecharts-like hierarchy and concurrency within basic function blocks (BFBs). Such features can significantly enhance function blocks and help create more succinct and readable specifications. We propose a new syntactic extension to the standard called hierarchical and concurrent execution control chart (HCECC). A major roadblock for any suggested changes to the standard is the need for compliance. Our approach extends the synchronous execution semantics of IEC 61499, where HCECCs are purely syntactic sugar. Using a revised synchronous semantics, our compiler generates standard compliant C code from HCECCs. Benchmarking and usability studies reveal the relative superiority of the proposed approach over existing approaches.

Ontological approach for DSL development

This paper presents a project whose main objective is to explore the ontological based development of Domain Specific Languages (DSL), more precisely, of their underlying Grammar. After reviewing the basic concepts characterizing Ontologies and DSLs, we introduce a tool, Onto2Gra, that takes profit of the knowledge described by the ontology and automatically generates a grammar for a DSL that allows to discourse about the domain described by that ontology. This approach represents a rigorous method to create, in a secure and effective way, a grammar for a new specialized language restricted to a concrete domain. The usual process of creating a grammar from the scratch is, as every creative action, difficult, slow and error prone; so this proposal is, from a grammar engineering point of view, of uttermost importance. After the grammar generation phase, the Grammar Engineer can manipulate it to add syntactic sugar to improve the final language quality or even to add specific semantic actions. The Onto2Gra project is composed of three engines. The main one is OWL2DSL, the component that converts an OWL ontology into a complete Attribute Grammar for the construction of an internal representation of all the input data. The two additional modules are Onto2OWL, converts ontologies written in OntoDL into standard OWL, and DDesc2OWL, converts domain instances written in the new DSL into the initial OWL ontology.

Hygienic resugaring of compositional desugaring

Syntactic sugar is widely used in language implementation. Its benefits are, however, offset by the comprehension problems it presents to programmers once their program has been transformed. In particular, after a transformed program has begun to evaluate (or otherwise be altered by a black-box process), it can become unrecognizable. We present a new approach to _resugaring_ programs, which is the act of reflecting evaluation steps in the core language in terms of the syntactic sugar that the programmer used. Relative to prior work, our approach has two important advances: it handles hygiene, and it allows almost arbitrary rewriting rules (as opposed to restricted patterns). We do this in the context of a DAG representation of programs, rather than more traditional trees.

Evaluating Strategies to Control Enzymatic Browning of Minimally Processed Yacon (Smallanthus sonchifolius)

To control enzymatic browning in minimally processed yacon (Smallanthus sonchifolius), strategies combining anti-browning agents and modified atmosphere were investigated. Yacon slices were immersed in anti-browning agent solutions—sodium metabisulfite (0.5 %), L-cysteine (0.5 %), or the acids lactic (1 %), malic (1 %), succinic (1 %), ethylenediaminetetraacetic (EDTA; 1 %), ascorbic (3 %), citric (3 %) or tartaric (3 %), or a control (0.5 % de sugar)—for 5 min, then packaged with air or modified atmosphere (N2) and stored at 5 °C. Sensory and physical-chemical (soluble solids, phenolic content, peroxidase activity, pH, color, instrumental texture, and mass variation) analyses were performed. For a given anti-browning agent, any significant difference was not found between yacon slices stored under air or N2. However, when comparing the different anti-browning agents, only ascorbic, citric, and tartaric acids were effective enzymatic browning inhibitors without significantly changing typical sensory attributes of yacon. Among them, tartaric acid is not often reported in literature for controlling enzymatic browning in vegetal products, contrarily to the two others.

Resugaring

Syntactic sugar is pervasive in language technology. It is used to shrink the size of a core language; to define domain-specific languages; and even to let programmers extend their language. Unfortunately, syntactic sugar is eliminated by transformation, so the resulting programs become unfamiliar to authors. Thus, it comes at a price: it obscures the relationship between the user's source program and the program being evaluated. We address this problem by showing how to compute reduction steps in terms of the surface syntax. Each step in the surface language emulates one or more steps in the core language. The computed steps hide the transformation, thus maintaining the abstraction provided by the surface language. We make these statements about emulation and abstraction precise, prove that they hold in our formalism, and verify part of the system in Coq. We have implemented this work and applied it to three very different languages.

The complexity of regular expressions and property paths in SPARQL

The World Wide Web Consortium (W3C) recently introduced property paths in SPARQL 1.1, a query language for RDF data. Property paths allow SPARQL queries to evaluate regular expressions over graph-structured data. However, they differ from standard regular expressions in several notable aspects. For example, they have a limited form of negation, they have numerical occurrence indicators as syntactic sugar, and their semantics on graphs is defined in a nonstandard manner. We formalize the W3C semantics of property paths and investigate various query evaluation problems on graphs. More specifically, let x and y be two nodes in an edge-labeled graph and r be an expression. We study the complexities of: (1) deciding whether there exists a path from x to y that matches r and (2) counting how many paths from x to y match r . Our main results show that, compared to an alternative semantics of regular expressions on graphs, the complexity of (1) and (2) under W3C semantics is significantly higher. Whereas the alternative semantics remains in polynomial time for large fragments of expressions, the W3C semantics makes problems (1) and (2) intractable almost immediately. As a side-result, we prove that the membership problem for regular expressions with numerical occurrence indicators and negation is in polynomial time.

Layout-sensitive language extensibility with SugarHaskell

Programmers need convenient syntax to write elegant and concise programs. Consequently, the Haskell standard provides syntactic sugar for some scenarios (e.g., do notation for monadic code), authors of Haskell compilers provide syntactic sugar for more scenarios (e.g., arrow notation in GHC), and some Haskell programmers implement preprocessors for their individual needs (e.g., idiom brackets in SHE). But manually written preprocessors cannot scale: They are expensive, error-prone, and not composable. Most researchers and programmers therefore refrain from using the syntactic notations they need in actual Haskell programs, but only use them in documentation or papers. We present a syntactically extensible version of Haskell, SugarHaskell, that empowers ordinary programmers to implement and use custom syntactic sugar. Building on our previous work on syntactic extensibility for Java, SugarHaskell integrates syntactic extensions as sugar libraries into Haskell's module system. Syntax extensions in SugarHaskell can declare arbitrary context-free and layout-sensitive syntax. SugarHaskell modules are compiled into Haskell modules and further processed by a Haskell compiler. We provide an Eclipse-based IDE for SugarHaskell that is extensible, too, and automatically provides syntax coloring for all syntax extensions imported into a module. We have validated SugarHaskell with several case studies, including arrow notation (as implemented in GHC) and EBNF as a concise syntax for the declaration of algebraic data types with associated concrete syntax. EBNF declarations also show how to extend the extension mechanism itself: They introduce syntactic sugar for using the declared concrete syntax in other SugarHaskell modules.