2,283 research outputs found

    Undergraduate Catalog of Studies, 2023-2024

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    Undergraduate Catalog of Studies, 2023-2024

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    Complete and easy type Inference for first-class polymorphism

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    The Hindley-Milner (HM) typing discipline is remarkable in that it allows statically typing programs without requiring the programmer to annotate programs with types themselves. This is due to the HM system offering complete type inference, meaning that if a program is well typed, the inference algorithm is able to determine all the necessary typing information. Let bindings implicitly perform generalisation, allowing a let-bound variable to receive the most general possible type, which in turn may be instantiated appropriately at each of the variable’s use sites. As a result, the HM type system has since become the foundation for type inference in programming languages such as Haskell as well as the ML family of languages and has been extended in a multitude of ways. The original HM system only supports prenex polymorphism, where type variables are universally quantified only at the outermost level. This precludes many useful programs, such as passing a data structure to a function in the form of a fold function, which would need to be polymorphic in the type of the accumulator. However, this would require a nested quantifier in the type of the overall function. As a result, one direction of extending the HM system is to add support for first-class polymorphism, allowing arbitrarily nested quantifiers and instantiating type variables with polymorphic types. In such systems, restrictions are necessary to retain decidability of type inference. This work presents FreezeML, a novel approach for integrating first-class polymorphism into the HM system, focused on simplicity. It eschews sophisticated yet hard to grasp heuristics in the type systems or extending the language of types, while still requiring only modest amounts of annotations. In particular, FreezeML leverages the mechanisms for generalisation and instantiation that are already at the heart of ML. Generalisation and instantiation are performed by let bindings and variables, respectively, but extended to types beyond prenex polymorphism. The defining feature of FreezeML is the ability to freeze variables, which prevents the usual instantiation of their types, allowing them instead to keep their original, fully polymorphic types. We demonstrate that FreezeML is as expressive as System F by providing a translation from the latter to the former; the reverse direction is also shown. Further, we prove that FreezeML is indeed a conservative extension of ML: When considering only ML programs, FreezeML accepts exactly the same programs as ML itself. # We show that type inference for FreezeML can easily be integrated into HM-like type systems by presenting a sound and complete inference algorithm for FreezeML that extends Algorithm W, the original inference algorithm for the HM system. Since the inception of Algorithm W in the 1970s, type inference for the HM system and its descendants has been modernised by approaches that involve constraint solving, which proved to be more modular and extensible. In such systems, a term is translated to a logical constraint, whose solutions correspond to the types of the original term. A solver for such constraints may then be defined independently. To this end, we demonstrate such a constraint-based inference approach for FreezeML. We also discuss the effects of integrating the value restriction into FreezeML and provide detailed comparisons with other approaches towards first-class polymorphism in ML alongside a collection of examples found in the literature

    Current and Future Challenges in Knowledge Representation and Reasoning

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    Knowledge Representation and Reasoning is a central, longstanding, and active area of Artificial Intelligence. Over the years it has evolved significantly; more recently it has been challenged and complemented by research in areas such as machine learning and reasoning under uncertainty. In July 2022 a Dagstuhl Perspectives workshop was held on Knowledge Representation and Reasoning. The goal of the workshop was to describe the state of the art in the field, including its relation with other areas, its shortcomings and strengths, together with recommendations for future progress. We developed this manifesto based on the presentations, panels, working groups, and discussions that took place at the Dagstuhl Workshop. It is a declaration of our views on Knowledge Representation: its origins, goals, milestones, and current foci; its relation to other disciplines, especially to Artificial Intelligence; and on its challenges, along with key priorities for the next decade

    “She takes rest as seriously as working:” How resilient professional caregivers think about and practice rest

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    Do resilient employees need less rest? This study explored that question by investigating how resilient professional caregivers think about and practice rest. Analysis revealed that highly communicatively resilient professional caregivers acknowledged the material reality of the body, labeled here bounded physicality. Bounded physicality is the limited ability to engage physically in space and time. A sample of highly communicatively resilient professional caregivers was collected using atypical survey-based case selection and standard deviation analysis. Eleven positively deviant (PD) caregivers and five corroborators were subsequently interviewed about their meanings and practices of rest. Additionally, five professionals who scored extremely low on the communicative resilience measure and four who were average were also interviewed as a validation effort. Constant comparative analysis of participants’ interview responses (N = 25) revealed that PD caregivers constructed rest as the proactive pursuit of holistic restoration and held a multifaceted interpretive schema of rest. Namely, they viewed rest as a (a) strategic defense and (b) normal indispensable joy, and practiced rest as (c) multimodal care. Additionally, they resisted the ideal worker norm (IWN) by protecting, prioritizing, and pursuing rest. Finally, PD caregivers experienced positive consequences of rest on their personal, relational, and professional wellbeing. As anticipated, these findings contrasted with non-PD caregivers’ interview responses. Taken together, this scholarship extends organizational communication theory, including literatures on positive organizational scholarship, the communicative theory of resilience, the ideal worker norm, and meanings of work (MOW) and rest. Ultimately, highly communicatively resilient professional caregivers build crucial reserves through rest, which challenges the view that resilient employees need less rest

    Knowledge Problems in Security Protocols: Going Beyond Subterm Convergent Theories

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    We introduce a new form of restricted term rewrite system, the graph-embedded term rewrite system. These systems, and thus the name, are inspired by the graph minor relation and are more flexible extensions of the well-known homeomorphic-embedded property of term rewrite systems. As a motivating application area, we consider the symbolic analysis of security protocols, and more precisely the two knowledge problems defined by the deduction problem and the static equivalence problem. In this field restricted term rewrite systems, such as subterm convergent ones, have proven useful since the knowledge problems are decidable for such systems. However, many of the same decision procedures still work for examples of systems which are "beyond subterm convergent". However, the applicability of the corresponding decision procedures to these examples must often be proven on an individual basis. This is due to the problem that they don\u27t fit into an existing syntactic definition for which the procedures are known to work. Here we show that many of these systems belong to a particular subclass of graph-embedded convergent systems, called contracting convergent systems. On the one hand, we show that the knowledge problems are decidable for the subclass of contracting convergent systems. On the other hand, we show that the knowledge problems are undecidable for the class of graph-embedded systems

    Minoritized Knowledges: Agency, Literature, Temporalities

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    Abstract “I am not erudite enough to be interdisciplinary, but I can break rules.” Gayatri Spivak, A Critique of Postcolonial Reason, xiii “Minoritized Knowledges: Agency, Literature, Temporalities,” queries an agency exercised by literature in excess of authorial intention as well as the text itself, which is transforming in its unoriginality, as a convergence of exploited, minoritized knowledges. The six chapters engage multiple fields as discourses rather than territories. “Nonidentity and Vectors of History,” brings Critical Theory’s notion of nonidentity into dialogue with key literary work by authors including Claudia Rankine and Elfriede Jelinek. The historical principle of nonidentity illuminates a convergence in their writing, which facilitates understanding history as vectors of trauma rather than modes of domination. Chapter 2. “Literary Agency and Minoritized Grammar'' addresses the political work of contemporary poets, including Fred Moten, contesting the sequestering of alternative minoritized grammars in poetic terms. Limiting alternative grammar to poetic experimentation perpetuates melancholy and epistemic hegemony. Chapter 3. “Economies of Sacrifice,” situates the work historically, where sacrifice emerges as central to western hegemonic logic. Recent feminist and queer mobilizations of the figure of Antigone highlight how sacrifice undergirds western tradition/s of exploitation and increasingly generates economies of violence that mobilize current knowledge markets. Chapter 4. “Unfinished Knowledge,” sets the stage by underscoring the convergence of partial, situated and unfinished knowledges in the works of Black, feminist and queer theorists for which literature is key. Such incomplete epistemologies continue to be underestimated and ambivalently received. Chapter 5. “The Folly of Narrative,” engages with current critical re-readings of literary realism, to draw out alternative epistemological figures and temporalities that contest the logic of sacrifice. Chapter 6. “Literary Agency and Minoritized Knowledges” revisits the history of western ideas decentering eurocentrism’s deployment of certainty qua mastery and completion under the guise of knowledge. Pivoting from the convergence of decolonial queer feminist critique, I elaborate alternative epistemological figures, including counter-grammar, nonidentity and folly. By undermining dominant dichotomous epistemologies and inviting diasporic study, these figures challenge epistemic injustice. The contrast between epistemologies of exploitation versus decolonization is not dichotomous but performative. Hence, it is situated, situational, contextual, temporal, historical and (dis)located

    Undergraduate Catalog of Studies, 2022-2023

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    A liberal-democratic theory of borders

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    My dissertation aims to intervene in to the debate on the legitimacy of border controls. Currently, the debate is inhabited by two main positions: the first one contesting the legitimacy of border controls on the basis of the principles of individual freedom and moral equality, the second one defending the legitimacy of border controls by referring to the idea of collective sovereignty. In my work I try to defend a position alternative to both perspectives. What I argue is that the legitimacy of border controls cannot be neither affirmed nor denied a priori. Rather, whether the exercise of border controls is legitimate depends on who approves them. In this perspective, I maintain that border controls are legitimate to the extent to which they are accepted within an ideal discursive situation in which both members of receiving communities and would-be migrants are included

    Query Rewriting with Disjunctive Existential Rules and Mappings

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    We consider the issue of answering unions of conjunctive queries (UCQs) with disjunctive existential rules and mappings. While this issue has already been well studied from a chase perspective, query rewriting within UCQs has hardly been addressed yet. We first propose a sound and complete query rewriting operator, which has the advantage of establishing a tight relationship between a chase step and a rewriting step. The associated breadth-first query rewriting algorithm outputs a minimal UCQ-rewriting when one exists. Second, we show that for any ``truly disjunctive'' nonrecursive rule, there exists a conjunctive query that has no UCQ-rewriting. It follows that the notion of finite unification sets (fus), which denotes sets of existential rules such that any UCQ admits a UCQ-rewriting, seems to have little relevance in this setting. Finally, turning our attention to mappings, we show that the problem of determining whether a UCQ admits a UCQ-rewriting through a disjunctive mapping is undecidable. We conclude with a number of open problems.Comment: This report contains the paper accepted at KR 2023 and an appendix with full proofs. 24 page
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