Type inference for unboxed types and first class mutability

Abstract

Systems programs rely on fine-grain control of data representation and use of state to achieve performance, conformance to hardware specification, and temporal predictability. The robustness and checkability of these programs could be greatly improved if modern type systems and programming language ideas, such as polymorphism and type inference, could be applied to these programs.BitC is a higher-order programming language in the tradition of ML and Haskell, extended to incorporate both state and the expression of unboxed and low-level datatypes. State and unboxed value types interact in subtle ways with polymorphic type-inference. Unless handled with care in the language design, interactions of these features can lead to unsoundness or results that are counter-intuitive to the programmer. Because instances of value types may have mutable components, a decision must be made concerning their compatibility at copy boundaries: should structurally equivalent types that differ only in their mutability be considered compatible. The choice impacts both the amount of polymorphism that the language can preserve and the burden of type annotation imposed on the programmer.This paper presents some of these challenges and our design for how to address these issues.

Operating system verification—An overview

“…One of the central features of this approach was to create a new programming language for kernel implementation firstone that is safe, clean, and suitable for verification and low-level implementation at the same time. The idea was not necessarily to invent new language features, but rather to pick and choose from existing research and combine the necessary features into a targeted language for implementing verified OS kernels (Sridhar & Shapiro 2006;Shapiro 2006). This is a farreaching and long-term effort, but one with great appeal: The main kernel languages assembler, C, and C++ are old, with many unsafe features and were not built to ease program verification.…”

“…Sridhar & Shapiro (2006) describe the language specification and a number of small innovations in its type system. The language is designed to be type safe and fast, and to allow reasoning about the low-level layout of data structures.…”

Sound and Complete Type Inference for a Systems Programming Language

“…Due to the above interaction of polymorphism and unboxed mutability, a traditional HM-style inference algorithm cannot defer decisions about the mutability of types past their generalization. Therefore, current algorithms fix the mutability of types before generalization based on certain heuristics -thus sacrificing completeness [22]. In order to alleviate this problem, we use a new form of constrained types that range over both mutability and polymorphism.…”

Programming language challenges in systems codes

“…BitC is a more comprehensive approach, and by and large we have not found that direct support for representation provides any interesting difficulties in of itself. The difficulty lies in simultaneous support for representation, state, and polymorphism, which is the subject of Sridhar's paper in the current proceedings [23]. In email exchanges, Diatchki has reported that his enhancement to Haskell has had a significant impact on the implementation of their prototype operating system.…”