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ion in Sather STEPHAN MURER, STEPHEN OMOHUNDRO, DAVID STOUTAMIRE, and CLEMENS SZYPERSKI International Computer Science Institute Sather extends the notion of an iterator in a powerful new way. We argue that iteration abstractions belong in class interfaces on an equal footing with routines. Sather iterators were derived from CLU iterators but are much more flexible and better suited for object-oriented programming. We retain the property that iterators are structured, i.e. strictly bound to a controlling structured statement. We motivate and describe the construct along with several simple examples. We compare it with iteration based on CLU iterators, cursors, riders, streams, series, generators, coroutines, blocks, closures, and lambda expressions. Finally, we describe experiences with iterators in the Sather compiler and libraries. Categories and Subject Descriptors: D.1.5 [Programming Techniques]: Object-oriented Programming; D.3.3 [Programming Languages]: Language Constructs and Fe...

Abstract. To introduce the republication of “Definitional Interpreters for Higher-Order Programming Languages”, the author recounts the circumstances of its creation, clarifies several obscurities, corrects a few mistakes, and briefly summarizes some more recent developments.

Abstract. We introduce an expressive yet semantically clean core Java-like language, Java Jr., and provide it with a formal operational semantics based on traces of observable actions which represent interaction across package boundaries. A detailed example based on the Observer Pattern is used to demonstrate the intuitive character of the semantic model. We also show that our semantic trace equivalence is fully-abstract with respect to a natural notion of testing equivalence for object systems. This is the first such result for a full class-based OO-language with inheritance. 1

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Non-local control transfer and exception handling have a long tradition in higher-order programming languages such as Common Lisp, Scheme and ML. However, each language stops short of providing a full and complementary approach --- control handling is provided only if the corresponding control operator is first-order. In this work, we describe handlers in a higher-order control setting. We invoke our earlier theoretical result that all denotational models of control languages invariably include capabilities that handle control. These capabilities, when incorporated into the language, form an elegant and powerful higher-order generalization of the first-order exception-handling mechanism. 1 Introduction Control manipulation in applicative programming languages comes in two flavors. First-order control operators allow computations to abort to a dynamically enclosing control context, e.g., Common Lisp's [23, 24] throw and ML's [9, 17] raise. They are invariably accompanied by forms th...

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ing and using (L-unif) we have that any two lambdas that are everywhere undefined are equivalent. The classic example of an everywhere undefined lambda is Bot 4 = x:app(x:app(x; x); x:app(x; x)) In f , another example of an everywhere undefined lambda is the "do-forever" loop. Do 4 = f:Yv(Dox:Do(f(x)) By the recursive definition, for any lambda ' and value v Do(')(v) \Gamma!Ø Do(')('(v)) Reasoning about Functions with Effects 21 In f , either '(v) \Gamma!Ø v 0 for some v 0 or '(v) is undefined. In the latter case the computation is undefined since the redex is undefined. In the former case, the computation reduces to Do(')(v 0 ) and on we go. The argument for undefinedness of Bot relies only on the (app) rule and will be valid in any uniform semantics. In contrast the argument for undefinedness of Do(') relies on the (fred.isdef) property of f . Functional Streams We now illustrate the use of (L-unif-sim) computation to reason about streams represented as functions ...

Sather iters are a powerful new way to encapsulate iteration. We argue that such iteration abstractions belong in a class' interface on an equal footing with its routines. Sather iters were derived from CLU iterators but are much more flexible and better suited for object-oriented programming. We motivate and describe the construct along with several simple examples. We compare it with iteration based on CLU iterators, cursors, riders, streams, series, generators, coroutines, blocks, closures, and lambda expressions. Finally, we describe how to implement them in terms of coroutines and then show how to transform this implementation into efficient code.

This paper describes the design and the semantics of MetaKlaim, an higher order distributed process calculus equipped with staging mechanisms. MetaKlaim integrates MetaML (an extension of SML for multi-stage programming) and Klaim (a Kernel Language for Agents Interaction and Mobility), to permit interleaving of meta-programming activities (like assembly and linking of code fragments), dynamic checking of security policies at administrative boundaries and "traditional" computational activities on a wide area network (like remote communication and code mobility). MetaKlaim exploits a powerful type system (including polymorphic types a la system F) to deal with highly parameterized mobile components and to dynamically enforce security policies: types are metadata which are extracted from code at run-time and are used to express trustiness guarantees.