An Indexed Linear Logic for Idempotent Intersection Types (Long version)

Indexed Linear Logic has been introduced by Ehrhard and Bucciarelli, it can be seen as a logical presentation of non-idempotent intersection types extended through the relational semantics to the full linear logic. We introduce an idempotent variant of Indexed Linear Logic. We give a fine-grained reformulation of the syntax by exposing implicit parameters and by unifying several operations on formulae via the notion of base change. Idempotency is achieved by means of an appropriate subtyping relation. We carry on an in-depth study of indLL as a logic, showing how it determines a refinement of classical linear logic and establishing a terminating cut-elimination procedure. Cut-elimination is proved to be confluent up to an appropriate congruence induced by the subtyping relation

The (In)Efficiency of interaction

Evaluating higher-order functional programs through abstract machines inspired by the geometry of the interaction is known to induce space efficiencies, the price being time performances often poorer than those obtainable with traditional, environment-based, abstract machines. Although families of lambda-terms for which the former is exponentially less efficient than the latter do exist, it is currently unknown how general this phenomenon is, and how far the inefficiencies can go, in the worst case. We answer these questions formulating four different well-known abstract machines inside a common definitional framework, this way being able to give sharp results about the relative time efficiencies. We also prove that non-idempotent intersection type theories are able to precisely reflect the time performances of the interactive abstract machine, this way showing that its time-inefficiency ultimately descends from the presence of higher-order types