Concept

Covariance and contravariance (computer science)

Related publications (21)

When Subtyping Constraints Liberate A Novel Type Inference Approach for First-Class Polymorphism

Lionel Emile Vincent Parreaux, Aleksander Slawomir Boruch-Gruszecki

Type inference in the presence of first-class or "impredicative" second-order polymorphism a la System F has been an active research area for several decades, with original works dating back to the end of the 80s. Yet, until now many basic problems remain ...

Assoc Computing Machinery2024

Type-Preserving Compilation of Class-Based Languages

Guillaume André Fradji Martres

The Dependent Object Type (DOT) calculus was designed to put Scala on a sound basis, but while DOT relies on structural subtyping, Scala is a fundamentally class-based language. This impedance mismatch means that a proof of DOT soundness by itself is ...

EPFL2023

A case for DOT: Theoretical Foundations for Objects with Pattern Matching and GADT-Style Reasoning

Yichen Xu, Lionel Emile Vincent Parreaux, Aleksander Slawomir Boruch-Gruszecki

Many programming languages in the OO tradition now support pattern matching in some form. Historical examples include Scala and Ceylon, with the more recent additions of Java, Kotlin, TypeScript, and Flow. But pattern matching on generic class hierarchies ...

Assoc Computing Machinery2022

Celsius: A Model for Safe Initialization of Objects

Martin Odersky, Fengyun Liu, Paolo Giosuè Giarrusso

Accessing uninitialized data during object initialization is a common and subtle programming error. This error is either not prevented by mainstream languages, like in Java, C++, Scala, or it is prevented by greatly restricting initialization patterns, lik ...

2020

The Simple Essence of Algebraic Subtyping: Principal Type Inference with Subtyping Made Easy

Lionel Emile Vincent Parreaux

MLsub extends traditional Hindley-Milner type inference with subtyping while preserving compact principal types, an exciting new development. However, its specification in terms of biunification is difficult to understand, relying on the new concepts of bi ...

2020

Quoted Staged Rewriting: A Practical Approach to Library-Defined Optimizations

Christoph Koch, Amir Shaikhha, Lionel Emile Vincent Parreaux

Staging has proved a successful technique for programmatically removing code abstractions, thereby allowing for faster program execution while retaining a high-level interface for the programmer. Unfortunately, techniques based on staging suffer from a num ...

ACM2017

Type Soundness for Dependent Object Types (DOT)

Tiark Rompf, Nada Amin

Scala's type system unifies aspects of ML modules, object-oriented, and functional programming. The Dependent Object Types (DOT) family of calculi has been proposed as a new theoretic foundation for Scala and similar expressive languages. Unfortunately, ty ...

Assoc Computing Machinery2016

Type Soundness for Dependent Object Types

Tiark Rompf, Nada Amin

Scala’s type system unifies aspects of ML modules, object-oriented, and functional programming. The Dependent Object Types (DOT) family of calculi has been proposed as a new theoretic foundation for Scala and similar expressive languages. Unfortunately, ty ...

2016

Decrypting Local Type Inference

Hubert Plociniczak

Statically typed languages verify programs at compile-time. As a result many programming mistakes are detected at an early stage of development. A programmer does not have to specify types for every single term manually, however. Many programming languages ...

EPFL2016

Self-Assembly: Lightweight Language Extension and Datatype Generic Programming, All-in-One!

Heather Christine Klug, Philipp Haller

In this paper we show a general mechanism, called self-assembly, for lightweight language extensions (LLEs). LLEs allow users to define generic operations or properties that operate over a large class of types. With LLEs it is possible, for example, for us ...

2014

Improving Human-Compiler Interaction Through Customizable Type Feedback

Martin Odersky, Heather Christine Klug, Hubert Plociniczak

Type errors reported by compilers can sometimes be cryptic, or difficult to understand. In this paper, we propose a type debugging framework that exposes a high-level representation of the typechecking decision-making process that users normally do not hav ...

2014

Foundations of Path-Dependent Types

Martin Odersky, Tiark Rompf, Nada Amin

A scalable programming language is one in which the same concepts can describe small as well as large parts. Towards this goal, Scala unifies concepts from object and module systems. An essential ingredient of this unification is the concept of objects wit ...

Assoc Computing Machinery2014

Programming with Numerical Uncertainties

Eva Darulova

Numerical software, common in scientific computing or embedded systems, inevitably uses an approximation of the real arithmetic in which most algorithms are designed. In many domains, roundoff errors are not the only source of inaccuracy and measurement as ...

EPFL2014

Lightweight Polymorphic Effects

Martin Odersky, Philipp Haller, Lukas Rytz

Type-and-effect systems are a well-studied approach for reasoning about the computational behavior of programs. Nevertheless, there is only one example of an effect system that has been adopted in a wide-spread industrial language: Java’s checked exception ...

Springer-Verlag2012

Finding Almost-Invariants in Distributed Systems

Dejan Kostic, Marco Canini, Maysam Yabandeh

It is notoriously hard to develop dependable distributed systems. This is partly due to the difficulties in foreseeing various corner cases and failure scenarios while implementing a system that will be deployed over an asynchronous network. In contrast, r ...

2011

Improving API Documentation for Java-like Languages

Gilles Dubochet, Donna Malayeri

The Javadoc paradigm for displaying API documentation to users is quite popular, with similar variants existing for many mainstream languages. However, two user interface design properties of Javadoc may reduce its utility when displaying documentation for ...

2010

Isolated Actors for Race-Free Concurrent Programming

Philipp Haller

Message-based concurrency using actors has the potential to scale from multicore processors to distributed systems. However, several challenges remain until actor-based programming can be applied on a large scale. First, actor implementations must be effic ...

EPFL2010

Capabilities for Uniqueness and Borrowing

Martin Odersky, Philipp Haller

An important application of unique object references is safe and efficient message passing in concurrent object-oriented programming. However, to prevent the ill effects of aliasing, practical systems often severely restrict the shape of messages passed by ...

Springer2010

Compiling Scala for Performance

Iulian Dragos

Scala is a new programming language bringing together object-oriented and functional programming. Its defining features are uniformity and extensibility. Scala offers great flexibility for programmers, allowing them to grow the language through libraries. ...

EPFL2010

Implementing First-Class Polymorphic Delimited Continuations by a Type-Directed Selective CPS-Transform

Martin Odersky, Tiark Rompf, Ingo Maier

We describe the implementation of first-class polymorphic delimited continuations in the programming language Scala. We use Scala's pluggable typing architecture to implement a simple type and effect system, which discriminates expressions with control eff ...

ACM2009