Decoding Lua: formal semantics for the developer and the semanticist

Abstract

We provide formal semantics for a large subset of the Lua programming language, in its version 5.2. We validate our model by mechanizing it and testing it against the test suite of the reference interpreter of Lua, con rming that our model accurately represents the language.In addition, we set us an ambitious goal: to target both a PL semanticist -not necessarily versed in Lua-, and a Lua developer -not necessarily versed in semantic frameworks. To the former, we present the peculiarities of the language, and how we model them in a traditional small-step operational semantics, embedded within Felleisen-Hieb's reduction semantics with evaluation contexts. e mechanization is, naturally, performed in PLT Redex, the de facto tool for mechanizing reduction semantics.To the reader unfamiliar with such concepts, we provide, to our best possible within the space limitations, a gentle introduction of the model. It is our hope that developers of the di erent Lua implementations and dialects understand the model and consider it both for testing their work and for experimenting with new language features. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for pro t or commercial advantage and that copies bear this notice and the full citation on the rst page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is

Comparison of ESP programming platforms

“…The Lua is an asynchronous and event-driven script language [16], [17]. Other languages are procedural that makes a clear flow of execution [18], [19]. Lua requires the asynchronous mode and other approaches to develop and structure their applications.…”

From Specification to Testing: Semantics Engineering for Lua 5.2

“…It also includes a variety of tools for testing them: unit testing, random generators of terms for random testing of properties, stepper for step-by-step reduction sequences. It has been successfully used for the mechanization of large semantics models of real programming languages (e.g., JavaScript Guha et al (2010); Politz et al (2012); Python Politz et al (2013); Scheme Matthews and Findler (2007); and Lua 5.2 Soldevila et al (2017Soldevila et al ( , 2020Soldevila et al ( , 2022); the development of tools for program analysis (like, again, Soldevila et al (2020), to check for a particular kind of well-behavedness of Lua 5.2 programs; Lorenzen and Erdweg (2013), for checking type-soundness of syntactic language extensions that introduces high-level programming concepts). Other, particular uses cases, involve the mechanization of operational semantics for virtual machines specialised for running reactive programs Oeyen et al (2022), or even mechanizing a model of Redex itself, as is done in Felleisen et al (2009).…”