928 research outputs found
A Reflection on Types
The ability to perform type tests at runtime blurs the line between statically-typed and dynamically-checked languages. Recent developments in Haskell’s type system allow even programs that use reflection to themselves be statically typed, using a type-indexed runtime representation of types called \{}\textit{TypeRep}. As a result we can build dynamic types as an ordinary, statically-typed library, on top of \{}\textit{TypeRep} in an open-world context
A Reflection on Types
The ability to perform type tests at runtime blurs the line between statically-typed and dynamically-checked languages. Recent developments in Haskell’s type system allow even programs that use reflection to themselves be statically typed, using a type-indexed runtime representation of types called \{}\textit{TypeRep}. As a result we can build dynamic types as an ordinary, statically-typed library, on top of \{}\textit{TypeRep} in an open-world context
Size-Change Termination as a Contract
Termination is an important but undecidable program property, which has led
to a large body of work on static methods for conservatively predicting or
enforcing termination. One such method is the size-change termination approach
of Lee, Jones, and Ben-Amram, which operates in two phases: (1) abstract
programs into "size-change graphs," and (2) check these graphs for the
size-change property: the existence of paths that lead to infinite decreasing
sequences.
We transpose these two phases with an operational semantics that accounts for
the run-time enforcement of the size-change property, postponing (or entirely
avoiding) program abstraction. This choice has two key consequences: (1)
size-change termination can be checked at run-time and (2) termination can be
rephrased as a safety property analyzed using existing methods for systematic
abstraction.
We formulate run-time size-change checks as contracts in the style of Findler
and Felleisen. The result compliments existing contracts that enforce partial
correctness specifications to obtain contracts for total correctness. Our
approach combines the robustness of the size-change principle for termination
with the precise information available at run-time. It has tunable overhead and
can check for nontermination without the conservativeness necessary in static
checking. To obtain a sound and computable termination analysis, we apply
existing abstract interpretation techniques directly to the operational
semantics, avoiding the need for custom abstractions for termination. The
resulting analyzer is competitive with with existing, purpose-built analyzers
Computer Aided Verification of Relational Models
Binary relational algebra provides semantic foundations for major areas of computing, such as database design, state-based modeling and functional programming. Remarkably, static checking support in these areas fails to exploit the full semantic content of relations. In particular, properties such as the simplicity or injectivity of relations are not statically enforced in operations such as database queries, state transitions, or composition of functional components.
When data models, their constraints and operations are represented by point-free binary relational expressions, proof obligations can be expressed as inclusions between relational expressions.We developed a type-directed, strategic term rewriting system that can be used to simplify relational proof obligations and ultimately reduce them to tautologies. Such reductions can be used to provide extended static checking for design contraints commonly found in software modeling and development.XIII Workshop IngenierÃa de Software (WIS).Red de Universidades con Carreras en Informática (RedUNCI
Dynamically typed languages
Dynamically typed languages such as Python and Ruby have experienced a rapid grown in popularity in recent times. However, there is much confusion as to what makes these languages interesting relative to statically typed languages, and little knowledge of their rich history. In this chapter I explore the general topic of dynamically typed languages, how they differ from statically typed languages, their history, and their defining features
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