Pallene: A companion language for Lua

Abstract

• We present Pallene, a typed and ahead-of-time-compiled subset of Lua. • Pallene has a simple and portable implementation that is still very efficient. • Pallene is an order of magnitude faster than Lua and as fast as a JIT compiler. • Pallene may be specially useful for performance-sensitive Lua extension modules. • Run-time tag checking is not incompatible with efficient typed code. The simplicity and flexibility of dynamic languages make them popular for prototyping and scripting, but the lack of compile-time type information makes it challenging to generate efficient executable code. Inspired by ideas from scripting, just-in-time compilers, and optional type systems, we have developed Pallene, a typed companion language to the Lua scripting language, intended for writing lower-level libraries and extension modules. It plays the role of a system language in the scripting paradigm, but one that has been explicitly designed to interoperate with Lua. Pallene is designed to be efficient, to interoperate seamlessly with Lua (even sharing its runtime), and to be familiar to Lua programmers. It should also be simple, easy to understand, and easy to implement, so it can be as portable as maintainable as Lua itself. In this paper, we discuss the rationale for Pallene's design and present a description of its syntax, type system, and semantics. We also compare the performance of Pallene extension modules against pure Lua (both interpreted and JIT-compiled), against C extension modules (operating with Lua data structures), and also against programs fully written in C, which provide a familiar baseline. The results corroborate our hypothesis that Pallene has the potential to be a low-level counterpart to Lua. The performance of Lua extension modules written in Pallene can be better than that of equivalent modules written in C and it is competitive with the performance from a JIT compiler, despite the vastly simpler implementation. This is a revised and extended version of a SBLP 2018 paper with a similar title [1] .