Localized Lama Gradual Typing

Gradual typing is a modern approach for combining benefits of static typing and dynamic typing. Although scientific research aim for soundness of type systems, many of languages intentionally make their type system unsound for speeding up performance. This paper describes an implementation of a dialect for Lama programming language that supports gradual typing with explicit annotation of dangerous parts of code. The target of current implementation is to grant type safety to programs while keeping their power of untyped expressiveness. This paper covers implementation issues and properties of created type system. Finally, some perspectives on improving precision and soundness of type system are discussed.

Putting Gradual Types to Work

In this paper, we describe our experience incorporating gradual types in a statically typed functional language with Hindley-Milner style type inference. Where most gradually typed systems aim to improve static checking in a dynamically typed language, we approach it from the opposite perspective and promote dynamic checking in a statically typed language. Our approach provides a glimpse into how languages like SML and OCaml might handle gradual typing. We discuss our implementation and challenges faced—specifically how gradual typing rules apply to our representation of composite and recursive types. We review the various implementations that add dynamic typing to a statically typed language in order to highlight the different ways of mixing static and dynamic typing and examine possible inspirations while maintaining the gradual nature of our type system. This paper also discusses our motivation for adding gradual types to our language, and the practical benefits of doing so in our industrial setting.

Enhanced type inference for binding-time analysis

In this paper we will be taking a look at type inference and its uses for binding-time analysis, dynamic typing and better error messages. We will propose a new binding-time analysis algorithm ℬ, which is a modification of an already existing algorithm by Gomard [4], and discuss the speed difference.

Gradual session types

Session types are a rich type discipline, based on linear types, that lifts the sort of safety claims that come with type systems to communications. However, web-based applications and microservices are often written in a mix of languages, with type disciplines in a spectrum between static and dynamic typing. Gradual session types address this mixed setting by providing a framework which grants seamless transition between statically typed handling of sessions and any required degree of dynamic typing. We propose Gradual GV as a gradually typed extension of the functional session type system GV. Following a standard framework of gradual typing, Gradual GV consists of an external language, which relaxes the type system of GV using dynamic types; an internal language with casts, for which operational semantics is given; and a cast-insertion translation from the former to the latter. We demonstrate type and communication safety as well as blame safety, thus extending previous results to functional languages with session-based communication. The interplay of linearity and dynamic types requires a novel approach to specifying the dynamics of the language.

Correctness of compiling polymorphism to dynamic typing

The connection between polymorphic and dynamic typing was originally considered by Curry et al. (1972, Combinatory Logic, vol. ii) in the form of “polymorphic type assignment” for untyped λ-terms. Types are assigned after the fact to what is, in modern terminology, a dynamic language. Interest in type assignment was revitalized by the proposals of Bracha et al. (1998, OOPSLA) and Bank et al. (1997, POPL) to enrich Java with polymorphism (generics), which in turn sparked the development of other languages, such as Scala, with similar combinations of features. In such a setting, where the target language already has a monomorphic type system, it is desirable to compile polymorphism to dynamic typing in such a way that as much static typing as possible is preserved, relying on dynamics only insofar as genericity is actually required. The basic approach is to compile polymorphism using embeddings from each type into a universal “top” type, ${\mathbb{D}}$, and partial projections that go in the other direction. This scheme is intuitively reasonable, and, indeed, has been used in practice many times. Proving its correctness, however, is non-trivial. This paper studies the compilation of System F to an extension of Moggi's computational meta-language with a dynamic type and shows how the compilation may be proved correct using a logical relation.