A practical unification of multi-stage programming and macros

Abstract

Program generation is indispensable. We propose a novel uni cation 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 o ers compile-time code generation. In this work we draw upon a long line of research on metaprogramming, starting with Lisp, MetaML and MetaO-Caml. We provide direct support for quotes, splices and toplevel 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 rst implements the Hidden Markov Model, Shonan Challenge for HPC. The second implements the staged streaming library Strymonas. CCS Concepts • Software and its engineering → Language features; Macro languages;

Semantics-preserving inlining for metaprogramming

“…The aforementioned syntactic mondalities are introduced to denote where the evaluation needs to be deferred and we already cross the boundary of semantics-preserving code. At this point, we can navigate and guide freely the process of generating code from a quoted domain-speci c language as shown in past work [6,10,13]. The macro system that comes in Scala 3, described in 5.4 essentially gains inspiration from these technologies and completes what we present in this work.…”

“…From this artifact, it is relatively simple to extract the original AST of the method. Quoted code fragments are also encoded [13] in TASTy.…”

“…This is the approach followed in Scala 3 [18]. It o ers a powerful set of metaprogramming constructs, including staging with quotes {..} and splices ${..} [3,5,13,17]. Quotes delay the execution of code while splices compute code that will be inserted in a larger piece of code.…”

Staging with class: a specification for typed template Haskell

“…Although our work is inspired by Haskell, there is reason to believe that it has wider applications. The recent release of Scala 3 added support for typed code quotations to the language [Stucki et al 2018]. Preliminary experiments suggest that these quotations suffer from surprising interactions with implicit arguments: implicit resolution within quotations sometimes fails mysteriously.…”

“…Since its introduction Sheard 1997, 2000] multi-stage programming with quotation has attracted both theoretical and practical interest. Several languages, including MetaOCaml [Kiselyov 2014], Haskell and Scala [Stucki et al 2018], include implementations of typed quotations.…”