Sound type-dependent syntactic language extension

Abstract

Syntactic language extensions can introduce new facilities into a programming language while requiring little implementation effort and modest changes to the compiler. It is typical to desugar language extensions in a distinguished compiler phase after parsing or type checking, not affecting any of the later compiler phases. If desugaring happens before type checking, the desugaring cannot depend on typing information and type errors are reported in terms of the generated code. If desugaring happens after type checking, the code generated by the desugaring is not type checked and may introduce vulnerabilities. Both options are undesirable. We propose a system for syntactic extensibility where desugaring happens after type checking and desugarings are guaranteed to only generate well-typed code. A major novelty of our work is that desugarings operate on typing derivations instead of plain syntax trees. This provides desugarings access to typing information and forms the basis for the soundness guarantee we provide, namely that a desugaring generates a valid typing derivation. We have implemented our system for syntactic extensibility in a languageindependent fashion and instantiated it for a substantial subset of Java, including generics and inheritance. We provide a sound Java extension for Scala-like for-comprehensions.

Exploration of language specifications by compilation to first-order logic

“…Our results can inform future applications of automated first-order theorem provers for reasoning about language specifications and type systems. We are currently applying ATPs for automatically proving type soundness of a language's dynamic semantics [19], of desugaring transformations [43,44], and of program transformations in general.…”

Semantic Query Integration With Reason

“…With DOTSpa, we require an extended type checker, so approaches relying solely on transformations of the AST are not suitable. Instead, the conceptual framework proposed in [32] is closer to our approach. Other systems for compiler extensions include Polyglot [36] and ExtendJ [15].…”

Creating Domain-Specific Languages by Composing Syntactical Constructs

“…SoundX [16] takes a di erent approach to macros: they rewrite type derivation trees instead of syntax trees. The resulting macros can be checked to introduce neither binding errors nor type errors.…”

“…A macro defines a new construct by expanding code into the host language, thus giving the illusion of a new language construct without the need to redefine the underlying language. The sophistication of a macro system varies from simple text expansion systems to systems using hygienic macros that enable correct name bindings [6,9] and macro systems with static types [13,16].…”