FreezeML:Complete and Easy Type Inference for First-Class Polymorphism

ML is remarkable in providing statically typed polymorphism without the programmer ever having to write any type annotations. The cost of this parsimony is that the programmer is limited to a form of polymorphism in which quantifiers can occur only at the outermost level of a type and type variables can be instantiated only with monomorphic types. Type inference for unrestricted System F-style polymorphism is undecidable in general. Nevertheless, the literature abounds with a range of proposals to bridge the gap between ML and System F. We put forth a new proposal, FreezeML, a conservative extension of ML with two new features. First, let- and lambda-binders may be annotated with arbitrary System F types. Second, variable occurrences may be frozen, explicitly disabling instantiation. FreezeML is equipped with type-preserving translations back and forth between System F and admits a type inference algorithm, an extension of algorithm W, that is sound and complete and which yields principal types.Comment: 48 pages, 23 Figures. Accepted for PLDI 202

Boxy Types: Inference for Higher-Rank Types and Impredicativity

Languages with rich type systems are beginning to employ a blend of type inference and type checking, so that the type inference engine is guided by programmer-supplied type annotations. In this paper we show, for the first time, how to combine the virtues of two well-established ideas: unification-based inference, and bidirectional propagation of type annotations. The result is a type system that conservatively extends Hindley-Milner, and yet supports both higher-rank types and impredicativity

Strong Normalization of MLF via a Calculus of Coercions

MLF is a type system extending ML with first-class polymorphism as in system F. The main goal of the present paper is to show that MLF enjoys strong normalization, i.e. it has no infinite reduction paths. The proof of this result is achieved in several steps. We first focus on xMLF, the Church-style version of MLF, and show that it can be translated into a calculus of coercions: terms are mapped into terms and instantiations into coercions. This coercion calculus can be seen as a decorated version of system F, so that the simulation results entails strong normalization of xMLF through the same property of system F. We then transfer the result to all other versions of MLF using the fact that they can be compiled into xMLF and showing there is a bisimulation between the two. We conclude by discussing what results and issues are encountered when using the candidates of reducibility approach to the same problem

Fossil trees, tree moulds and tree casts in the Palaeocene Mull Lava Field, NW Scotland: context, formation and implications for lava emplacement

Megafossils and macrofossils of terrestrial plants (trees, leaves, fruiting bodies, etc.) are found in sedimentary and pyroclastic units interbedded with lavas in many ancient lava fields worldwide, attesting to subaerial environments of eruption and the establishment of viable plant communities during periods of volcanic quiescence. Preservation within lava is relatively rare and generally confined to the more robust woody tissues of trees, which are then revealed in the form of charcoal, mineralised tissue or as trace fossil moulds (tree moulds) and casts of igneous rock (tree casts, s.s.). In this contribution, we document several such fossil trees (s.l.), and the lavas with which they are associated, from the Palaeocene Mull Lava Field (MLF) on the Isle of Mull, NW Scotland. We present the first detailed geological account of a unique site within the Mull Plateau Lava Formation (MPLF) at Quinish in the north of the island and provide an appraisal of the famous upright fossil tree – MacCulloch's Tree – remotely located on the Ardmeanach Peninsula on the west coast of the island, and another large upright tree (the Carsaig Tree) near Malcolm's Point in the district of Brolass, SW Mull; both occurring within the earlier Staffa Lava Formation (SLF). The taphonomy of these megafossils, along with palynological and lithofacies assessments of associated strata, allows speculation of likely taxonomic affinity and the duration of hiatuses supporting the establishment of forest/woodland communities. The Ardmeanach and Carsaig specimens, because of their size and preservation as upright (? in situ) casts enveloped by spectacularly columnar-jointed basaltic lava, appear to be unique. The aspect of these trees, the thickness of the enveloping lavas and the arrangement of cooling joints adjacent to the trees, implies rapid emplacement, ponding and slow, static cooling of voluminous and highly fluid basaltic magma. The specimens from Quinish include two prostrate casts and several prostrate moulds that collectively have a preferred orientation, aligning approximately perpendicular to that of the regional Mull Dyke Swarm, the putative fissure source of the lavas, suggesting local palaeo-flow was directed towards the WSW. The Quinish Lava is an excellent example of a classic pāhoehoe (compound-braided) type, preserving some of the best examples of surface and internal features so far noted from the Hebridean Igneous Province (HIP) lava fields. These Mull megafossils are some of the oldest recorded examples, remarkably well preserved, and form a significant feature of the island's geotourism industry

Cross-generational linguistic variation in the Canberra Vietnamese heritage language community: A corpus-centred investigation

This dissertation investigates cross-generational linguistic differences in the Canberra Vietnamese bilingual community, with a particular focus on Vietnamese as the heritage language. Specifically, it documents the vernacular and considers key aspects of this data from different theoretical perspectives. Its main contribution is an insight into a rarely studied heritage language variety in a contact community that has never been examined. The dissertation consists of five core chapters, organised into two parts. In the first part (Chapters 2–3), I describe how I documented the vernacular and created the Canberra Vietnamese English Corpus (CanVEC), an original corpus compiled specifically for this study that is also the first to be freely available for research purposes. The corpus consists of over ten hours of spontaneous speech produced by 45 Vietnamese-English bilingual speakers across two generations living in Canberra. In the second part of the study (Chapters 4–6), I put the corpus to use and investigate aspects of the cross-generational differences in Vietnamese as the heritage language in this community. In particular, I first probe the Vietnamese heritage language via its participation in the code-switching discourse (Chapter 4). In doing so, I focus on the applicability of the Matrix Language Framework (MLF) (Myers-Scotton, 1993, 2002) and its associated Matrix Language (ML) Turnover Hypothesis (Myers-Scotton, 1998) to the code-switching data in CanVEC. Since support for this prominent model has mainly come from language pairs that have different clausal word order or vastly different inventories of inflectional morphology, Vietnamese-English as a pair in which both languages are SVO and essentially isolating offers a tantalising testing ground for its application. Results show that the universal claims of this model do not hold so straight-forwardly. CanVEC data challenges several assumptions of the MLF, with the model ultimately only being able to account for around half of the CanVEC code-switching data. I further demonstrate that even when the ML is putatively identifiable and a cross-generational ML ‘turnover’ is quantitatively observed, the predictions do not reflect the direction of structural influence that we see in CanVEC. The MLF approach therefore sheds only limited light on cross-generational language shift and variation in this community. Given that null elements emerge as a distinct area of difficulty in Chapter 4, I take this aspect as the focal point for the next part of the investigation (Chapter 5), where I use the variationist approach (Labov, 1972 et seq.) to explore three cases where null and overt realisation alternates in Vietnamese: subjects, objects, and copulas. In doing so, I move away from the bilingual portion of CanVEC to examine the monolingual heritage Vietnamese subset directly. Results show that Vietnamese null subjects vary significantly across generations, while null objects and copulas remain stable in terms of use. As speakers also overwhelmingly prefer overt forms over null forms (∼70:30) across all the three of the variables of interest, I appeal to the generative interface-oriented approach (Sorace & Filiaci, 2006 et seq.) to next examine the distribution of overt subjects, objects, copulas (Chapter 6). These results converge with what was found for null forms: cross-generational effects were observed for pronominal subjects, but not pronominal objects and copulas. This finding also supports the importance of a distinction drawn in previous works between internal (syntax-semantics) and external (syntax-discourse/pragmatics) interface phenomena, with the latter being seemingly more susceptible to change. Ultimately, this dissertation highlights the empirical and theoretical value of studying rarely considered contact varieties, while deploying an integrated approach that acknowledges the multi-faceted complexity of the contact communities where these varieties are spoken.Cambridge Trust International Scholarshi

A case study of syntactic patterns of Egyptian Colloquial Arabic-English code-switching

The present study investigated the structural patterns of Egyptian Colloquial Arabic (ECA)-English code-switching in the domains of classroom and interviews at the American University in Cairo (AUC) by applying Pieter Muysken\u27s typology of code-mixing and relating it to the work of Poplack (1980) and Myers-Scotton (1993). It also aimed to stand on the nature of inflectional derivational and close-classed morphemes affixed to code-switched lexical items. The nature of the study was descriptive exploratory in which textual linguistic analysis was employed to analyze audio-recorded verbal data. The data was collected by observing four undergraduate classrooms held by the Department of English Language Instruction at AUC and conducting three focus group interviews with AUC graduate students. The results indicated that insertion pattern was more frequent in both domains, followed by alternation and congruent lexicalization (CL), which occurred more frequently in the interview domain. The results also showed that ECA definite article il- was utilized with English nouns in the insertion and CL patterns in both domains. While verb inflections were affixed to ECA verbs in classroom domain and to English verbs in the interview domain. The results indicated the use of English as the matrix language in classroom domain and the variation of the matrix language between ECA and English in the interview domain

An analysis of Estonian gaming streamers’ English-Estonian code-switching

Examining contact effects in language use helps to better understand contact-induced language change as well as the interaction between specific languages. The parallel use of at least two languages in one utterance is called code-switching. The use of code-switching allows for structural and semantic impact, which may result in new and interesting combinations. This MA thesis discusses English-Estonian code-switching in the Estonian online gaming community with the aim of answering two research questions: how do Estonian gamers use English code-switches in their Estonian utterances and can a cross-modal effect of code-switching be determined.https://www.ester.ee/record=b5428151*es

Ontogenesis of visual processing circuits in the zebrafish: analysis of specific neuronal subpopulations in development

The Zebrafish (Danio rerio) larva is an ideal model for identification of neuronal circuits such as those associated with visually guided behaviors like the optomotor and the optokinetic responses. The use of larvae expressing the calcium level indicator GCaMP in particular neuronal subpopulations allows monitoring of activity of these neurons and facilitates their anatomical and functional characterization. Our goal, in this context, is to characterize some of these subpopulations taking advantage of the expression of GFP using the Gal4-UAS system during the first 6 days of development. To examine and characterize the GFP expression in zebrafish larvae, we have applied an immunofluorescence protocol and recorded anatomical stacks using confocal imaging. This information gathered from several equivalent individuals and registered to a reference brain may then be used to establish anatomical atlases at these early stages of development that will complement those already developed for the 6 dpf larvae. Characterization of the transgenic lines at the early stages will help us to locate the functional clusters identified at 6 dpf with more anatomical accuracy and precision. We will present our work focusing on zebrafish lines, generated using a BAC transgenic approach, that expresses GFF or GFP from an insertion next to the olig2, chrna4 and pcp4a promoter regions. Two of these lines (olig2: GFP and chrna4: GFF) are shown to represent a similar pattern of expression has the original gene, whilst the pcp4a: GFF line does not, although its characterization is still of use to complement functional maps of neuron activity. In addition, we are using time lapse imaging with Lightsheet microscopy to follow the dynamics of neuronal differentiation and extension of projections during the 20-48 hours post fertilization period on an already characterized line(Chat:GFF)

Probe the transport function of ABCA3 by metabolic labelling of choline phospholipids

The ATP-binding cassette sub-family A member 3 (ABCA3) plays a critical role in the lipid metabolism of pulmonary surfactant. Locating on the outer membrane of the storage and secretion compartment of surfactant in alveolar type II cells, the lamellar bodies (LBs), ABCA3 is responsible for transporting phospholipids from the cytoplasm into the LBs. Mutations of ABCA3 were identified from patients suffering from neonatal respiratory distress syndrome (RDS) and childhood interstitial lung diseases (chILD). Therefore, exploring the functional assays of ABCA3 is in great demand for pathophysiology investigation and treatment researching. In the present study, wild type and variants of ABCA3 were expressed in A549 epithelial cells to probe mechanisms for transport activity of ABCA3. To quantify the function of ABCA3 alleles, we employed the choline analogue propargyl-Cho. Propargyl-Cho was taken up and the resultant phospholipids can be detected using a combination of click chemistry, fluorescence derivatization and microscopy to visualize and quantify the phospholipid end product. The accumulation of labeled phospholipids was time, concentration dependent. The detection of signal was dependent on choline kinase to incorporate the label into cellular phospholipids. Miltefosine, another substrate of ABCA3 can compete with the transport of propargyl-Cho. Finally, we showed that mutations (p.N568D and p.L1580P) in the ATP-binding cassette of ABCA3 impaired transport function of propargyl-Cho into intracellular vesicles. The present thesis addressed a novel method to assess structure-function relationships of ABCA3