Simplicity: A New Language for Blockchains

TL;DR

Simplicity is a new, Turing-incomplete functional language designed for blockchain applications, offering formal semantics, resource analysis, and expressiveness suitable for smart contracts, improving upon existing crypto languages.

Contribution

It introduces Simplicity, a formal, resource-analyzable language for blockchains that avoids loops and recursion, with semantics verified in Coq and an operational model called the Bit Machine.

Findings

Formal denotational semantics in Coq

Resource bounds can be statically derived

Expresses all finitary functions for smart contracts

Abstract

Simplicity is a typed, combinator-based, functional language without loops and recursion, designed to be used for crypto-currencies and blockchain applications. It aims to improve upon existing crypto-currency languages, such as Bitcoin Script and Ethereum's EVM, while avoiding some of the problems they face. Simplicity comes with formal denotational semantics defined in Coq, a popular, general purpose software proof assistant. Simplicity also includes operational semantics that are defined with an abstract machine that we call the Bit Machine. The Bit Machine is used as a tool for measuring the computational space and time resources needed to evaluate Simplicity programs. Owing to its Turing incompleteness, Simplicity is amenable to static analysis that can be used to derive upper bounds on the computational resources needed, prior to execution. While Turing incomplete, Simplicity can express any finitary function, which we believe is enough to build useful "smart contracts" for blockchain applications.