208 research outputs found
Reconciling positional and nominal binding
We define an extension of the simply-typed lambda calculus where two
different binding mechanisms, by position and by name, nicely coexist. In the
former, as in standard lambda calculus, the matching between parameter and
argument is done on a positional basis, hence alpha-equivalence holds, whereas
in the latter it is done on a nominal basis. The two mechanisms also
respectively correspond to static binding, where the existence and type
compatibility of the argument are checked at compile-time, and dynamic binding,
where they are checked at run-time.Comment: In Proceedings ITRS 2012, arXiv:1307.784
Competition between local erasure and long-range spreading of a single biochemical mark leads to epigenetic bistability
The mechanism through which cells determine their fate is intimately related
to the spreading of certain biochemical (so-called epigenetic) marks along
their genome. The mechanisms behind mark spreading and maintenance are not yet
fully understood, and current models often assume a long-range infection-like
process for the dynamics of marks, due to the polymeric nature of the chromatin
fibre which allows looping between distant sites. While these existing models
typically consider antagonising marks, here we propose a qualitatively
different scenario which analyses the spreading of a single mark. We define a
1D stochastic model in which mark spreading/infection occurs as a long-range
process whereas mark erasure/recovery is a local process, with an enhanced rate
at boundaries of infected domains. In the limiting case where our model
exhibits absorbing states, we find a first-order-like transition separating the
marked/infected phase from the unmarked/recovered phase. This suggests that our
model, in this limit, belongs to the long-range compact directed percolation
universality class. The abrupt nature of the transition is retained in a more
biophysically realistic situation when a basal infection/recovery rate is
introduced (thereby removing absorbing states). Close to the transition there
is a range of bistability where both the marked/infected and unmarked/recovered
states are metastable and long lived, which provides a possible avenue for
controlling fate decisions in cells. Increasing the basal infection/recovery
rate, we find a second transition between a coherent (marked or unmarked)
phase, and a mixed, or random, one.Comment: 11 pages, 7 figures, 2 appendice
Constrained Polymorphic Types for a Calculus with Name Variables
We extend the simply-typed lambda-calculus with a mechanism for dynamic rebinding of code based on parametric nominal interfaces. That is, we introduce values which represent single fragments, or families of named fragments, of open code, where free variables are associated with names which do not obey alpha-equivalence. In this way, code fragments can be passed as function arguments and manipulated, through their nominal interface, by operators such as rebinding, overriding and renaming. Moreover, by using name variables, it is possible to write terms which are parametric in their nominal interface and/or in the way it is adapted, greatly enhancing expressivity. However, in order to prevent conflicts when instantiating name variables, the name-polymorphic types of such terms need to be equipped with simple {inequality} constraints. We show soundness of the type system
Decentralizing MAS Monitoring with DecAMon
We describe DecAMon, an algorithm for decentralizing the monitoring of the MAS communicative behavior described via an Agent Interaction Protocol (AIP). If some agents in the MAS are grouped together and monitored by the same monitor, instead of individually, a partial decentralization of the monitoring activity can still be obtained even if the "unique point of choice" (a.k.a. local choice) and "connectedness for sequence" (a.k.a. causality) coherence conditions are not satisfied by the protocol.
Given an AIP specification, DecAMon outputs a set of "Monitoring Safe Partitions" of the agents, namely partitions P which ensure that having one monitor in charge for each group of agents in P allows detection of all and only the protocol violations that a fully centralized monitor would detect.
In order to specify AIPs we use "trace expressions": this formalism can express event traces that are not context-free and can model both synchronous and asynchronous communication just by changing the underlying notion of event
Modeling Infinite Behaviour by Corules
open3openDavide Ancona; Francesco Dagnino; Elena ZuccaAncona, Davide; Dagnino, Francesco; Zucca, Elen
Agents interoperability via conformance modulo mapping
We present an algorithm for establishing a flexible conformance relation between two local agent interaction protocols (LAIPs) based on mappings involving agents and messages, respectively. Conformance is in fact computed "modulo mapping": two LAIPs \u3c4 and \u3c4 may involve different agents and use different syntax for messages, but may still be found to be conformant provided that a given map from entities appearing in \u3c4 to corresponding entities in \u3c4 is applied. LAIPs are modelled as trace expressions whose high expressive power allows for the design of protocols that could not be specified using finite state automata or equivalent formalisms. This expressive power makes the problem of stating if \u3c4 conforms to \u3c4 undecidable. We cope with this problem by over-approximating trace expressions that may lead to infinite computations, obtaining a sound but not complete implementation of the proposed conformance check
Structural resolution for abstract compilation of object-oriented languages
We propose abstract compilation for precise static type analysis of
object-oriented languages based on coinductive logic programming. Source code
is translated to a logic program, then type-checking and inference problems
amount to queries to be solved with respect to the resulting logic program. We
exploit a coinductive semantics to deal with infinite terms and proofs produced
by recursive types and methods. Thanks to the recent notion of structural
resolution for coinductive logic programming, we are able to infer very precise
type information, including a class of irrational recursive types causing
non-termination for previously considered coinductive semantics. We also show
how to transform logic programs to make them satisfy the preconditions for the
operational semantics of structural resolution, and we prove this step does not
affect the semantics of the logic program.Comment: In Proceedings CoALP-Ty'16, arXiv:1709.0419
Semantic Subtyping for Non-Strict Languages
Semantic subtyping is an approach to define subtyping relations for type systems featuring union and intersection type connectives. It has been studied only for strict languages, and it is unsound for non-strict semantics. In this work, we study how to adapt this approach to non-strict languages: in particular, we define a type system using semantic subtyping for a functional language with a call-by-need semantics. We do so by introducing an explicit representation for divergence in the types, so that the type system distinguishes expressions that are results from those which are computations that might diverge
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