Abstract not found

doi:10.1017/S0956796809990219

Abstract. Ariola and Felleisen’s call-by-need λ-calculus replaces a variable occurrence with its value at the last possible moment. To support this gradual notion of substitution, function applications—once established—are never discharged. In this paper we show how to translate this notion of reduction into an abstract machine that resolves variable references via the control stack. In particular, the machine uses the static address of a variable occurrence to extract its current value from the dynamic control stack.

Abstract. We study call-by-need from the point of view of the duality between call-by-name and call-by-value. We develop sequent-calculus style versions of call-by-need both in the minimal and classical case. As a result, we obtain a natural extension of call-by-need with control operators. This leads us to introduce a call-by-need λµ-calculus. Finally, by using the dualities principles of λµ˜µ-calculus, we show the existence of a new call-by-need calculus, which is distinct from call-by-name, call-byvalue and usual call-by-need theories.

Abstract. The existing call-by-need λ calculi describe lazy evaluation via equational logics. A programmer can use these logics to safely ascertain whether one term is behaviorally equivalent to another or to determine the value of a lazy program. However, neither of the existing calculi models evaluation in a way that matches lazy implementations. Both calculi suffer from the same two problems. First, the calculi never discard function calls, even after they are completely resolved. Second, the calculi include re-association axioms even though these axioms are merely administrative steps with no counterpart in any implementation. In this paper, we present an alternative axiomatization of lazy evaluation using a single axiom. It eliminates both the function call retention problem and the extraneous re-association axioms. Our axiom uses a grammar of contexts to describe the exact notion of a needed computation. Like its predecessors, our new calculus satisfies consistency and standardization properties and is thus suitable for reasoning about behavioral equivalence. In addition, we establish a correspondence between our semantics and Launchbury’s natural semantics.