Closures in Lua

First-class functions are a very powerful language construct and a fundamental feature in functional languages. However, few procedural languages support this feature, due to their stack-based implementation. In this paper we discuss a new algorithm for the implementation of first-class functions used in the implementation of Lua 5.x. Unlike previous techniques, our algorithm does not need static analysis of the source code (a luxury that the on-the-fly Lua code generator cannot afford) and does not prevent the use of an array-based stack to store regular local variables.