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A Monadic Framework for Delimited Continuations
 UNDER CONSIDERATION FOR PUBLICATION IN J. FUNCTIONAL PROGRAMMING
"... Delimited continuations are more expressive than traditional abortive continuations and they apparently require a framework beyond traditional continuationpassing style (CPS). We show that this is not the case: standard CPS is sufficient to explain the common control operators for delimited continu ..."
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Delimited continuations are more expressive than traditional abortive continuations and they apparently require a framework beyond traditional continuationpassing style (CPS). We show that this is not the case: standard CPS is sufficient to explain the common control operators for delimited continuations. We demonstrate this fact and present an implementation as a Scheme library. We then investigate a typed account of delimited continuations that makes explicit where control effects can occur. This results in a monadic framework for typed and encapsulated delimited continuations, which we design and implement as a Haskell library.
Soutei, a LogicBased TrustManagement System System Description
"... Abstract. We describe the design and implementation of a trustmanagement system Soutei, a dialect of Binder, for access control in distributed systems. Soutei policies and credentials are written in a declarative logicbased security language and thus constitute distributed logic programs. Soutei p ..."
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Abstract. We describe the design and implementation of a trustmanagement system Soutei, a dialect of Binder, for access control in distributed systems. Soutei policies and credentials are written in a declarative logicbased security language and thus constitute distributed logic programs. Soutei policies are modular, concise, and readable. They support policy verification, and, despite the simplicity of the language, express role and attributebased access control lists, and conditional delegation. We describe the realworld deployment of Soutei into a publishsubscribe web service with distributed and compartmentalized administration, emphasizing the often overlooked aspect of authorizing the creation of resources and the corresponding policies. Soutei brings Binder from a research prototype into the real world. Supporting large, truly distributed policies required nontrivial changes to Binder, in particular moderestriction and goaldirected topdown evaluation. To improve the robustness of our evaluator, we describe a fair and terminating backtracking algorithm.
Kleene Monads: Handling Iteration in a Framework of Generic Effects
"... Abstract. Monads are a wellestablished tool for modelling various computational effects. They form the semantic basis of Moggi’s computational metalanguage, the metalanguage of effects for short, which made its way into modern functional programming in the shape of Haskell’s donotation. Standard c ..."
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Abstract. Monads are a wellestablished tool for modelling various computational effects. They form the semantic basis of Moggi’s computational metalanguage, the metalanguage of effects for short, which made its way into modern functional programming in the shape of Haskell’s donotation. Standard computational idioms call for specific classes of monads that support additional control operations. Here, we introduce Kleene monads, which additionally feature nondeterministic choice and Kleene star, i.e. nondeterministic iteration, and we provide a metalanguage and a sound calculus for Kleene monads, the metalanguage of control and effects, which is the natural joint extension of Kleene algebra and the metalanguage of effects. This provides a framework for studying abstract program equality focussing on iteration and effects. These aspects are known to have decidable equational theories when studied in isolation. However, it is well known that decidability breaks easily; e.g. the Horn theory of continuous Kleene algebras fails to be recursively enumerable. Here, we prove several negative results for the metalanguage of control and effects; in particular, already the equational theory of the unrestricted metalanguage of control and effects over continuous Kleene monads fails to be recursively enumerable. We proceed to identify a fragment of this language which still contains both Kleene algebra and the metalanguage of effects and for which the natural axiomatisation is complete, and indeed the equational theory is decidable. 1
Pure, Declarative, and Constructive Arithmetic Relations (Declarative Pearl) ⋆
"... Abstract. We present decidable logic programs for addition, multiplication, division with remainder, exponentiation, and logarithm with remainder over the unbounded domain of natural numbers. Our predicates represent relations without mode restrictions or annotations. They are fully decidable under ..."
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Abstract. We present decidable logic programs for addition, multiplication, division with remainder, exponentiation, and logarithm with remainder over the unbounded domain of natural numbers. Our predicates represent relations without mode restrictions or annotations. They are fully decidable under the common, DFSlike, SLD resolution strategy of Prolog or under an interleaving refinement of DFS. We prove that the evaluation of our arithmetic goals always terminates, given arguments that share no logic variables. Further, the (possibly infinite) set of solutions for a goal denotes exactly the corresponding mathematical relation. (For SLD without interleaving, and for some infinite solution sets, only half of the relation’s domain may be covered.) We define predicates to handle unary (for illustration) and binary representations of natural numbers, and prove termination and completeness of these predicates. Our predicates are written in pure Prolog, without cut (!), var/1, or other nonlogical operators. The purity and minimalism of our approach allows us to declare arithmetic in other logic systems, such as Haskell type classes. 1
A Monadic Framework for Delimited Continuations
"... Delimited continuations are more expressive than traditional abortive continuations and they apparently require a framework beyond traditional continuationpassing style (CPS). We show that this is not the case: standard CPS is sufficient to explain the common control operators for delimited continu ..."
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Delimited continuations are more expressive than traditional abortive continuations and they apparently require a framework beyond traditional continuationpassing style (CPS). We show that this is not the case: standard CPS is sufficient to explain the common control operators for delimited continuations. We demonstrate this fact and present an implementation as a Scheme library. We then investigate a typed account of delimited continuations that makes explicit where control effects can occur. This results in a monadic framework for typed and encapsulated delimited continuations, which we design and implement as a Haskell library. 1