User-Defined Operators Including Name Binding for New Language Constructs

Abstract

User-defined syntax extensions are useful to implement an embedded domain specific language (EDSL) with good code readability. They allow EDSL authors to define domain-natural notation, which is often different from the host language syntax. Recently, there have been several research works of powerful user-defined syntax extensions.One promising approach uses user-defined operators. A user-defined operator is a function with userdefined syntax. It can be regarded as a syntax extension implemented without macros. An advantage of userdefined operators is that an operator can be statically typed. The compiler can find type errors in the definition of an operator before the operator is used. In addition, the compiler can resolve syntactic ambiguities by using static types. However, language constructs involving static name binding are difficult to implement with userdefined operators. Name binding is an association between names and values (or memory locations). Our inquiry is whether we can design a system for user-defined operators involving a new custom name binding.This paper proposes a variant of a lambda expression, called a context-sensitive expression. A contextsensitive expression looks like a normal expression but it implicitly takes parameters. To realize user-defined name binding, these parameters are accessed through public members such as methods and operators of a parameter object instead of through parameter names. Programmers can emulate name binding by such methods or operators, for example, they can emulate a local variable through a getter operator and a setter operator. We also present turnstile type to give a type to a context-sensitive expression, DSL class to cooperate with syntax extension, and generic name to recognize arbitrary names given by users.A contribution of this paper is that we reveal that we can integrate a system for managing names and their scopes with the module system and type system of an object-oriented language such as Java. Programmers can define new language constructs involving custom name binding and other programmers can use them by importing modules. The compiler can statically verify the types of both the definition and usage of the language constructs.We have implemented ProteaJ2, a programming language based on Java, and it supports our proposal. We describe a parsing method that adopts eager disambiguation for fast parsing and discuss its time complexity. To show the practicality of our proposal, we have conducted two micro benchmarks to see the performance of our compiler. We also show several use cases of DSL classes for demonstrating DSL classes can express various language constructs.Our ultimate goal is to let programmers add any kind of new language construct to a host language. To do this, programmers should be able to define new syntax, name binding, and type systems within the host language. This paper shows that programmers can define name binding with their own syntax. ACM CCS 2012Software and its engineering → Extensible languages;

Generating a Generic Fluent API in Java

“…SugarJ [11] provides a method for extending Java syntax. ProteaJ [19], Wyvern [24], and Honu [26] are programming languages that natively support syntax extension. Using these syntax extension mechanisms, domain-specific notation can be embedded as is.…”