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This paper presents the syntax and reduction rules for an abstract machine based on the JavaScript XML language. We incorporate the notion of cost into our reduction rules, and create a type system that over-approximate this cost. This over-approximation results in an equation that may contain unknowns originating from while loops. We conclude with a formal proof of soundness of the type system for our abstract machine, demonstrating that it over-approximates the cost of any terminating program. An implementation of the type system, constraint gathering, and the abstract machine is also presented, Comment: Benjamin Bennetzen: 0009-0007-1751-6862 Daniel Vang Kleist: 0009-0005-1785-2124 Emilie Sonne Steinmann: 0009-0000-4733-5842 Loke Walsted: 0009-0002-1758-4594 Nikolaj Rossander Kristensen: 0009-0005-2339-8247 Peter Buus Steffensen: 0009-0005-6410-5869

Protecting confidential data from leaking is a critical challenge in computer systems, particularly given the growing number of observers on the internet. Therefore, limiting information flow using robust security policies becomes increasingly vital. We focus on the non-interference policy, where the goal is to ensure that confidential data can not impact public data. This paper presents a type system, for a subset of the ReScript syntax, designed to enforce non-interference. We conclude with a proof of soundness for the type system, demonstrating that if an expression is type-able, it is inherently non-interferent. In addition, we provide a brief overview of a type checker that implements the previously mentioned type system., Comment: Benjamin Bennetzen: 0009-0007-1751-6862 Daniel Vang Kleist: 0009-0005-1785-2124 Emilie Sonne Steinmann: 0009-0000-4733-5842 Loke Walsted: 0009-0002-1758-4594 Nikolaj Rossander Kristensen: 0009-0005-2339-8247 Peter Buus Steffensen: 0009-0005-6410-5869