{"ID":2832977,"CreatedAt":"2026-06-01T04:54:23.091178241Z","UpdatedAt":"2026-06-01T04:54:23.091178241Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2512.04755","arxiv_id":"2512.04755","title":"Typing Fallback Functions: A Semantic Approach to Type Safe Smart Contracts","abstract":"This paper develops semantic typing in a smart-contract setting to ensure type safety of code that uses statically untypable language constructs, such as the fallback function. The idea is that the creator of a contract on the blockchain equips code containing such constructs with a formal proof of its type safety, given in terms of the semantics of types. Then, a user of the contract only needs to check the validity of the provided 'proof certificate' of type safety. This is a form of proof-carrying code, which naturally fits with the immutable nature of the blockchain environment. As a concrete application of our approach, we focus on ensuring information flow control and non-interference for TinySol, a distilled version of the Solidity language, through security types. We provide the semantics of types in terms of a typed operational semantics of TinySol and we express the proofs of safety as coinductively-defined typing interpretations, which can be represented compactly via up-to techniques, similar to those used for bisimilarity. We also show how our machinery can be used to type the typical pointer-to-implementation pattern based on the fallback function and to reject a distilled version of the infamous Parity Multisig Wallet Attack.","short_abstract":"This paper develops semantic typing in a smart-contract setting to ensure type safety of code that uses statically untypable language constructs, such as the fallback function. The idea is that the creator of a contract on the blockchain equips code containing such constructs with a formal proof of its type safety, giv...","url_abs":"https://arxiv.org/abs/2512.04755","url_pdf":"https://arxiv.org/pdf/2512.04755v2","authors":"[\"Stian Lybech\",\"Daniele Gorla\",\"Luca Aceto\"]","published":"2025-12-04T12:45:23Z","proceeding":"cs.PL","tasks":"[\"cs.PL\"]","methods":"[]","has_code":false}