Abstract This paper introduces the QCheck-STM plugin for Ortac, a framework for dynamic verification of OCaml code. Ortac/QCheck-STM consumes OCaml module signatures annotated with behavioural specification contracts expressed in the Gospel language, extracts a functional model of a mutable data structure from it, and generates code for automated runtime assertion checking. We report on the implementation of the tool, the structure of the generated code, and on errors found in established OCaml libraries.

Batteryless energy-harvesting devices enable computing in inaccessible environments, at a cost to programmability and correctness. These devices operate intermittently as energy is available, using a recovery system to save and restore state. Some program tasks must execute atomically w.r.t. power failures, re-executing if power fails before completion. Any re-execution should typically be idempotent —its behavior should match the behavior of a single execution. Thus, a key aspect of correct intermittent execution is identifying and recovering state causing undesired non-idempotence. Unfortunately, past intermittent systems take an ad-hoc approach, using unsound dataflow analyses or conservatively recovering all written state. Moreover, no prior work allows the programmer to directly specify idempotence requirements (including allowable non-idempotence). We present curricle, the first type system approach to safe intermittence, for Rust. Type level reasoning allows programmers to express requirements and retains alias information crucial for sound analyses. Curricle uses information flow and type qualifiers to reject programs causing undesired non-idempotence. We implement Curricle’s type system on top of Rust’s compiler, evaluating the prototype on benchmarks from prior work. We find that Curricle benefits application programmers by allowing them to express idempotence requirements that are checked to be satisfied, and that targeting programs checked with Curricle allows intermittent system designers to write simpler recovery systems that perform better.