On the Relation between Context-Free Grammars and Parsing Expression Grammars

Context-Free Grammars (CFGs) and Parsing Expression Grammars (PEGs) have several similarities and a few differences in both their syntax and semantics, but they are usually presented through formalisms that hinder a proper comparison. In this paper we present a new formalism for CFGs that highlights the similarities and differences between them. The new formalism borrows from PEGs the use of parsing expressions and the recognition-based semantics. We show how one way of removing non-determinism from this formalism yields a formalism with the semantics of PEGs. We also prove, based on these new formalisms, how LL(1) grammars define the same language whether interpreted as CFGs or as PEGs, and also show how strong-LL(k), right-linear, and LL-regular grammars have simple language-preserving translations from CFGs to PEGs

Left Recursion in Parsing Expression Grammars

Parsing Expression Grammars (PEGs) are a formalism that can describe all deterministic context-free languages through a set of rules that specify a top-down parser for some language. PEGs are easy to use, and there are efficient implementations of PEG libraries in several programming languages. A frequently missed feature of PEGs is left recursion, which is commonly used in Context-Free Grammars (CFGs) to encode left-associative operations. We present a simple conservative extension to the semantics of PEGs that gives useful meaning to direct and indirect left-recursive rules, and show that our extensions make it easy to express left-recursive idioms from CFGs in PEGs, with similar results. We prove the conservativeness of these extensions, and also prove that they work with any left-recursive PEG. PEGs can also be compiled to programs in a low-level parsing machine. We present an extension to the semantics of the operations of this parsing machine that let it interpret left-recursive PEGs, and prove that this extension is correct with regards to our semantics for left-recursive PEGs.Comment: Extended version of the paper "Left Recursion in Parsing Expression Grammars", that was published on 2012 Brazilian Symposium on Programming Language

Few Versatile vs. Many Specialized Collections: How to design a collection library for exploratory programming?

While an integral part of all programming languages, the design of collection libraries is rarely studied. This work briefly reviews the collection libraries of 14 languages to identify possible design dimensions. Some languages have surprisingly few but versatile collections, while others have large libraries with many specialized collections. Based on the identified design dimensions, we argue that a small collection library with only a sequence, a map, and a set type are a suitable choice to facilitate exploratory programming. Such a design minimizes the number of decisions programmers have to make when dealing with collections, and it improves discoverability of collection operations. We further discuss techniques that make their implementation practical from a performance perspective. Based on these arguments, we conclude that languages which aim to support exploratory programming should strive for small and versatile collection libraries

Programming in Lua

Lua is spreading more and more throughout different areas of software, from embedded systems and mobile devices to the Web and the Internet of Things. Besides, it has a major role in the game industry, where knowledge of Lua has become an indisputable asset. Lua is the language of choice for anyone who needs a scripting language that is simple, efficient, extensible, portable, and free. Programming in Lua is the official book about the language, providing a solid base to any programmer who wants to use Lua. Authored by Roberto Ierusalimschy, the chief architect of the language, it covers all aspects of Lua 5---from the basics to its API with C. The book is the main source of programming patterns for Lua, with numerous code examples that help the reader to make the most of Lua's flexibility and powerful mechanisms. Programming in Lua is targeted at people with some programming background, but does not assume any prior knowledge about Lua or other scripting languages. This Fourth Edition updates the book to Lua 5.3 and marks a complete reorganization of the text. Building on his many years of experience teaching Lua, Roberto has restructured the book to present the material in a growing order of complexity, allowing the reader to better absorb the character of the language

Categories and Subject Descriptors K.2 [HISTORY OF

We report on the birth and evolution of Lua and discuss how it moved from a simple configuration language to a versatile, widely used language that supports extensible semantics, anonymous functions, full lexical scoping, proper tail calls, and coroutines