Typestates to Automata and back: a tool

Abstract

Development of software is an iterative process. Graphical tools to represent the relevant entities and processes can be helpful. In particular, automata capture well the intended execution flow of applications, and are thus behind many formal approaches, namely behavioral types. Typestate-oriented programming allow us to model and validate the intended protocol of applications, not only providing a top-down approach to the development of software, but also coping well with compositional development. Moreover, it provides important static guarantees like protocol fidelity and some forms of progress. Mungo is a front-end tool for Java that associates a typestate describing the valid orders of method calls to each class, and statically checks that the code of all classes follows the prescribed order of method calls. To assist programming with Mungo, as typestates are textual descriptions that are terms of an elaborate grammar, we developed a tool that bidirectionally converts typestates into an adequate form of automata, providing on one direction a visualization of the underlying protocol specified by the typestate, and on the reverse direction a way to get a syntactically correct typestate from the more intuitive automata representation.

Research Challenges in Orchestration Synthesis

“…Similarly to CARE, the runtime environment for contract automata [6], in Mungo finite state automata are used as behaviour assigned to Java classes (one automaton per class), with transition labels corresponding to methods of the classes. A tool to translate typestates into automata was presented at ICE 2020 [26]. CATApp, a graphical front-end tool for designing contract automata, is available in [19].…”

A Runtime Environment for Contract Automata

“…Other approaches to connect implementations with behavioural types (e.g., behavioural contracts, session types) are surveyed in [2,21]. Our approach is closer to [22,28], where behavioural types are expressed as finite state automata of Mungo, called typestates [27]. The toolchain of Mungo and StMungo is proposed to implement behavioural types specifications.…”

Retrofitting Typestates into Rust

“…We use the enumeration to represent the non-deterministic nature of the transition [12], as well as force the user to match against both cases. This enumeration has a few rules; all variants must be of Unit type 13 , and they must also share their identifier with an existing state.…”

“…get_color). Our PlantUML representation resembles Deterministic Object Automata [12], using diamonds to represent the possible outcomes of an operation.…”