1,605 research outputs found
Trust, but Verify: Two-Phase Typing for Dynamic Languages
A key challenge when statically typing so-called dynamic languages is the
ubiquity of value-based overloading, where a given function can dynamically
reflect upon and behave according to the types of its arguments. Thus, to
establish basic types, the analysis must reason precisely about values, but in
the presence of higher-order functions and polymorphism, this reasoning itself
can require basic types. In this paper we address this chicken-and-egg problem
by introducing the framework of two-phased typing. The first "trust" phase
performs classical, i.e. flow-, path- and value-insensitive type checking to
assign basic types to various program expressions. When the check inevitably
runs into "errors" due to value-insensitivity, it wraps problematic expressions
with DEAD-casts, which explicate the trust obligations that must be discharged
by the second phase. The second phase uses refinement typing, a flow- and
path-sensitive analysis, that decorates the first phase's types with logical
predicates to track value relationships and thereby verify the casts and
establish other correctness properties for dynamically typed languages
The Essence of Nested Composition
Calculi with disjoint intersection types support an introduction form for intersections called the merge operator, while retaining a coherent semantics. Disjoint intersections types have great potential to serve as a foundation for powerful, flexible and yet type-safe and easy to reason OO languages. This paper shows how to significantly increase the expressive power of disjoint intersection types by adding support for nested subtyping and composition, which enables simple forms of family polymorphism to be expressed in the calculus. The extension with nested subtyping and composition is challenging, for two different reasons. Firstly, the subtyping relation that supports these features is non-trivial, especially when it comes to obtaining an algorithmic version. Secondly, the syntactic method used to prove coherence for previous calculi with disjoint intersection types is too inflexible, making it hard to extend those calculi with new features (such as nested subtyping). We show how to address the first problem by adapting and extending the Barendregt, Coppo and Dezani (BCD) subtyping rules for intersections with records and coercions. A sound and complete algorithmic system is obtained by using an approach inspired by Pierce\u27s work. To address the second problem we replace the syntactic method to prove coherence, by a semantic proof method based on logical relations. Our work has been fully formalized in Coq, and we have an implementation of our calculus
Partial type constructors: Or, making ad hoc datatypes less ad hoc
This work is licensed under a Creative Commons Attribution 4.0 International License.Functional programming languages assume that type constructors are total. Yet functional programmers know better: counterexamples range from container types that make limiting assumptions about their contents (e.g., requiring computable equality or ordering functions) to type families with defining equations only over certain choices of arguments. We present a language design and formal theory of partial type constructors, capturing the domains of type constructors using qualified types. Our design is both simple and expressive: we support partial datatypes as first-class citizens (including as instances of parametric abstractions, such as the Haskell Functor and Monad classes), and show a simple type elaboration algorithm that avoids placing undue annotation burden on programmers. We show that our type system rejects ill-defined types and can be compiled to a semantic model based on System F. Finally, we have conducted an experimental analysis of a body of Haskell code, using a proof-of-concept implementation of our system; while there are cases where our system requires additional annotations, these cases are rarely encountered in practical Haskell code
Accessible user interface support for multi-device ubiquitous applications: architectural modifiability considerations
The market for personal computing devices is rapidly expanding from PC, to mobile, home entertainment systems, and even the automotive industry. When developing software targeting such ubiquitous devices, the balance between development costs and market coverage has turned out to be a challenging issue. With the rise of Web technology and the Internet of things, ubiquitous applications have become a reality. Nonetheless, the diversity of presentation and interaction modalities still drastically limit the number of targetable devices and the accessibility toward end users. This paper presents webinos, a multi-device application middleware platform founded on the Future Internet infrastructure. Hereto, the platform's architectural modifiability considerations are described and evaluated as a generic enabler for supporting applications, which are executed in ubiquitous computing environments
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