Proof of Multi-Stage Programming with Generative and Analytical Macros

In metaprogramming, code generation and code analysis are complementary. Traditionally, principled metaprogramming extensions for programming languages, like MetaML and BER MetaOCaml, offer strong foundations for code generation but lack equivalent support for code analysis. Similarly, existing macro systems are biased towards the code generation aspect. In this work, we present a calculus for macros featuring both code generation and code analysis. The calculus directly models separate compilation of macros, internalizing a commonly neglected aspect of macros. The system ensures that the generated code is well-typed and hygienic. We implement our system in Scala 3, provide a formalization, and prove its soundness.

Scala Macros, a Technical Report

Eugene Burmako, Martin Odersky

Metaprogramming is a powerful technique of software development, which allows to automate program generation. Applications of metaprogramming range from improving expressiveness of a programming language via deep embedding of domain-specific languages to boosting performance of produced code by providing programmer with finegrained control over compilation. In this report we introduce macros, facility that enables compile-time metaprogramming in the Scala programming language.

2012

Unification of Compile-Time and Runtime Metaprogramming in Scala

Eugene Burmako

Metaprogramming is a technique that consists in writing programs that treat other programs as data. This paradigm of software development contributes to a multitude of approaches that improve programmer productivity, including code generation, program analysis and domain-specific languages. Many programming languages and runtime systems provide support for metaprogramming. Programming platforms often distinguish the notions of compile-time and runtime metaprogramming, depending on the phase of the program lifecycle when metaprograms execute. It is common for different lifecycle phases to be hosted in different environ- ments, so it is also common for different kinds of metaprogramming to provide different capabilities to metaprogrammers. In this dissertation, we present an exploration of the idea of unifying compile-time and runtime metaprogramming in Scala. We focus on the practical aspect of the exploration; most of the described designs are available as popular software products, and some of them have become part of the standard distribution of Scala. First, guided by the motivation to consolidate disparate metaprogramming techniques available in earlier versions of Scala, we introduce scala.reflect, a unified metaprogram- ming framework that uses a language model derived from the Scala compiler to run metaprograms both at compile time and at runtime. Secondly, armed by the newfound metaprogramming powers, we describe Scala macros, a language-integrated compile-time metaprogramming facility based on scala.reflect. Thanks to the comprehensive nature of scala.reflect, macros are able to work with both syntactic and semantic information about Scala programs, enabling a wide range of previously impractical or impossible use cases. Finally, based on our experience and user feedback, we identify key strengths and weaknesses of scala.reflect and macros. We propose scala.meta, a new unified metapro- gramming framework, and inline/meta, a new macro system based on scala.meta, that take the best from their predecessors and address the most important problems.

EPFL2017

A Practical Unification of Multi-stage Programming and Macros

Martin Odersky, Nicolas Alexander Stucki

Program generation is indispensable. We propose a novel unification of two existing metaprogramming techniques: multi-stage programming and hygienic generative macros. The former supports runtime code generation and execution in a type-safe manner while the latter offers compile-time code generation. In this work we draw upon a long line of research on metaprogramming, starting with Lisp, MetaML and MetaOCaml. We provide direct support for quotes, splices and top-level splices, all regulated uniformly by a level-counting Phase Consistency Principle. Our design enables the construction and combination of code values for both expressions and types. Moreover, code generation can happen either at runtime à la MetaML or at compile time, in a macro fashion, à la MacroML. We provide an implementation of our design in Scala and we present two case studies. The first implements the Hidden Markov Model, Shonan Challenge for HPC. The second implements the staged streaming library Strymonas.

2018

Unification of Compile-Time and Runtime Metaprogramming in Scala

Eugene Burmako

EPFL2017