Auto-Collections for Scala | EPFL Graph Search

Modern programming languages such as Scala, Java and C# make extensive use of collections. A collection implementation represents a fixed choice in the dimensions of operation time and space utilization. Using the collection in a manner not consistent with this fixed choice can cause significant performance degradation. Often programmers have to choose between under-performing generic collection and specific data-structures at the cost of modularity and ex- tensibility. In his paper, we present and evaluate a generic collection library that automatically choose the appropriate collection implementations for an application. We implemented our solution in the Dotty compiler for Scala and showed that our implementation can choose optimal collections for com- mon basic algorithms.

Implementing Extensible Compilers

Martin Odersky, Matthias Zenger

New extensions to programming languages are constantly being proposed. But implementing these extensions usually turns out to be a very difficult and expensive task, since conventional compilers often lack extensibility and reusability. In this paper we present some fundamental techniques to implement extensible compilers in an object-oriented language. For being able to implement extensible compiler passes, we introduce an extensible form of algebraic datatypes. Our extensible algebraic datatypes with defaults yield a simple programming protocol for implementing extensible and reusable compiler passes in a functional style. We propose an architectural design pattern Context-Component which is specifically targeted towards building extensible, hierarchically composed systems. Our software architecture for extensible compilers combines the use of algebraic types, known from functional languages, with this object-oriented design pattern. We show that this approach enables us to extend existing compilers flexibly without modifying any source code. Our techniques have been successfully applied in the implementation of the extensible Java compiler JaCo.

2001

Two approaches to portable macros

Eugene Burmako, Fengyun Liu

For any programming language that supports macros and has multiple implementations (each with different AST definitions), there is a common problem: how to make macros that operate on ASTs portable among different compiler implementations? Implementing portable macros is especially important for statically typed languages like Scala, as IDE vendors usually have different implementations of the language in order to support rich IDE features. Unportable macros compromise IDE features and degrade programming experience. We describe two approaches to the portability problem based on two different views on macros: (1) the tree-based approach, which views macros as operations on abstract syntax trees, solves the problem by defining standard abstract syntax trees; (2) the syntax-based approach, which views macros as operations on abstract syntax, solves the problem by defining standard abstract syntax. We show that the latter has significant practical advantages, especially in supporting semantic macros that use type information of ASTs to transform user code. Based on the idea, we implemented a new macro system, Gestalt, for the experimental Scala compiler, Dotty. The new implementation solves several long-standing problems of the current Scala macro system and demonstrates advantages over alternative approaches. Our solution has been adopted in the official new Scala macro system.

2017

Design and implementation of an optimizing type-centric compiler for a high-level language

Dmytro Petrashko

Production compilers for programming languages face multiple requirements. They should be correct, as we rely on them to produce code. They should be fast, in order to provide a good developer experience. They should also be easy to maintain and evolve. This thesis shows how an expressive high level type system can be used to simplify the development of a compiler and demonstrates this on a compiler for Scala. First, it shows how expressive types of high level languages can be used to build internal data structures that provide a statically checked API, ensuring that important properties hold at compile time. Second, we also show how high level language features can be used to abstract the components of a compiler. We demonstrate this by introducing a type-safe layer on top of the bytecode emission phase. This makes it possible to abstract away the implementation details of the compiler frontend and run the same bytecode emission phase in two different Scala compilers. Third, it presents MiniPhases, a novel way to organize transformation passes in a compiler. MiniPhases impose constraints on the organization of passes that are beneficial for maintainability, performance, and testability. We include a detailed performance evaluation of MiniPhases which indicates that their speedup is due to improved cache friendliness and to a lower rate of promotions of objects into the old generations of garbage collectors. Finally, we demonstrate how the expressive type system of the language being compiled can be used for static analysis. We present a novel call graph construction algorithm which uses the typing context for context sensitivity. The resulting algorithm is both substantially faster and more precise than existing alternatives. We demonstrate the applicability of this analysis by extending common subexpression elimination to idempotent expression elimination.

EPFL2017

Design and implementation of an optimizing type-centric compiler for a high-level language

Dmytro Petrashko

EPFL2017