Symbolic execution (SE) tools often rely on intermediate languages (ILs) to support multiple programming languages, promising reusability and efficiency. In practice, this approach introduces trade-offs between performance, accuracy, and language feature support. We argue that building SE engines directly for each source language is both simpler and more effective. We present Soteria, a lightweight OCaml library for writing SE engines in a functional style, without compromising on performance, accuracy or feature support. Soteria enables developers to construct SE engines that operate directly over source-language semantics, offering configurability, compositional reasoning, and ease of implementation. Using Soteria, we develop Soteria-Rust, the first Rust SE engine supporting TreeBorrows (the intricate aliasing model of Rust), and Soteria-C, a compositional SE engine for C. Both tools are competitive with or outperform state-of-the-art tools such as Kani, Infer.Pulse, CBMC and Gillian-C in performance and the number of bugs detected. We formalise the theoretical foundations of Soteria and prove its soundness, demonstrating that sound, efficient, accurate, and expressive SE can be achieved without the compromises of ILs.

@article{paperbot3715,
  title = {Soteria: Efficient Symbolic Execution as a Functional Library: Perhaps You Should Write Your Own Symbolic Execution Engine!},
  author = {Sacha-Élie Ayoun and Opale Sjöstedt and Azalea Raad},
  journal = {Proceedings of the ACM on Programming Languages},
  volume = {10},
  number = {PLDI},
  year = {2026},
  doi = {10.1145/3808306}
}