Computing and Information Systems - Research Publications
Permanent URI for this collection
Search Results
1 - 3 of 3
-
ItemA theory of overloading(ASSOC COMPUTING MACHINERY, 2005-11)We present a novel approach to allow for overloading of identifiers in the spirit of type classes. Our approach relies on a combination of the HM(X) type system framework with Constraint Handling Rules (CHRs). CHRs are a declarative language for writing incremental constraint solvers, that provide our scheme with a form of programmable type language. CHRs allow us to precisely describe the relationships among overloaded identifiers. Under some sufficient conditions on the CHRs we achieve decidable type inference and the semantic meaning of programs is unambiguous. Our approach provides a common formal basis for many type class extensions such as multiparameter type classes and functional dependencies.
-
ItemWhen do bounds and domain propagation lead to the same search space?(ASSOC COMPUTING MACHINERY, 2005-05)This article explores the question of when two propagation-based constraint systems have the same behavior, in terms of search space. We categorize the behavior of domain and bounds propagators for primitive constraints, and provide theorems that allow us to determine propagation behaviors for conjunctions of constraints. We then show how we can use this to analyze CLP(FD) programs to determine when we can safely replace domain propagators by more efficient bounds propagators without increasing search space. Empirical evaluation shows that programs optimized by the analysis' results are considerably more efficient.
-
ItemEfficient Constraint Propagation Engines(ASSOC COMPUTING MACHINERY, 2008-12)This article presents a model and implementation techniques for speeding up constraint propagation. Three fundamental approaches to improving constraint propagation based on propagators as implementations of constraints are explored: keeping track of which propagators are at fixpoint, choosing which propagator to apply next, and how to combine several propagators for the same constraint. We show how idempotence reasoning and events help track fixpoints more accurately. We improve these methods by using them dynamically (taking into account current variable domains to improve accuracy). We define priority-based approaches to choosing a next propagator and show that dynamic priorities can improve propagation. We illustrate that the use of multiple propagators for the same constraint can be advantageous with priorities, and introduce staged propagators that combine the effects of multiple propagators with priorities for greater efficiency.