TOWARDS MODELS OF REALISTIC COMPUTING MACHINES IN COMPUTER SCIENCE

The paper presents an approach to system modelling in design of both hardware and software systems. It is based on the definition of models of machines that can be directly implemented. The paper shows how to render less abstract and more realistic the abstract machines defined by theoreticians, so that they can capture implementation and technological-oriented aspects, such as testability, and allow an easy transition to final implementations. A realistic abstract machine for lambda-calculus is then presented and the design of system for lambda-expressions evaluation is illustrated. The architecture chosen for the system is based on a collection of finite state automata, evolving concurrently and communicating via a broadcast system. Some conclusive remarks about the use of realistic models arc finally drawn

Abstract Machine for a Comonadic Dataflow Language

The formal semantics of higher-order functional dataflow language programs can be represented with the concepts of arrows and comonads from category theory. Both of these methods convey the meaning of programs, but not the operational behaviour of them. In order to understand the operational behaviour of dataflow programs we will derive an abstract machine from an interpreter that is equivalent to a comonadic denotational semantics of a higher-order call-by-name dataflow language. The resulting abstract machine is identical to the well known abstract machine by Krivine with the exception of an overloaded notion of the environment and two additional transition rules for evaluating constructs specific to the dataflow language. The main result of this thesis is that the operational behaviour of call-by-name dataflow language programs is identical to the operational behaviour of regular non-strict languages

The complexity of two finite-state models, optimizing transducers and counting automata

An optimizing finite-state transducer is a nondeterministic finite-state transducer in which states are either maximizing or minimizing. In a given state, the optimal output is the maximum or minimum--over all possible transitions--of the transition output concatenated with the optimal output of the resulting state. The ranges of optimizing finite-state transducers form a class in NL which includes a hierarchy based on the number of alternations of maximizing and minimizing states in a computation. The inequivalence problem--whether or not two transducers compute different functions, and the range inequivalence problem are shown to be undecidable. Some other problems associated with this model are shown to be complete for NL and NP;A counting finite-state automaton is a nondeterministic finite-state automaton which, on an input over its input alphabet, (magically) writes in binary the number of accepting computations on the input. We examine the complexity of computing the counting function of an NFA, and the complexity of recognizing its range as a set of binary strings. We also consider the pumping behavior of counting finite-state automata. The class of functions computed by counting NFAs (1) includes a class of functions computed by deterministic finite-state transducers; (2) is contained in the class of functions computed by polynomially time- and linearly space-bounded Turing transducers; (3) includes a function whose range is the composite numbers

On Computational Small Steps and Big Steps: Refocusing for Outermost Reduction

We study the relationship between small-step semantics, big-step semantics and abstract machines, for programming languages that employ an outermost reduction strategy, i.e., languages where reductions near the root of the abstract syntax tree are performed before reductions near the leaves.In particular, we investigate how Biernacka and Danvy's syntactic correspondence and Reynolds's functional correspondence can be applied to inter-derive semantic specifications for such languages.The main contribution of this dissertation is three-fold:First, we identify that backward overlapping reduction rules in the small-step semantics cause the refocusing step of the syntactic correspondence to be inapplicable.Second, we propose two solutions to overcome this in-applicability: backtracking and rule generalization.Third, we show how these solutions affect the other transformations of the two correspondences.Other contributions include the application of the syntactic and functional correspondences to Boolean normalization.In particular, we show how to systematically derive a spectrum of normalization functions for negational and conjunctive normalization

Atlas of sensations - on sensibilities in a computational design practice

The driving force behind the body of work of SPAN is defined by the application of advanced computational design methodologies. This dissertation can be understood as a cartography (in the best tradition of an atlas) of the work of the practice from its founding year 2003 until 2017 - a period profoundly shaped by the progress made in technological advances. These technological means allow SPAN to discuss architectural project through a series of different lenses such as conceptualization, planning, fabrication to the maintenance of the designed objects, through the use of emerging technical opportunities wither this be the interrogation of novel geometries (Blocks, Ore, Barcelona Recursion), computational methods of rationalization (Expo Façade) or advanced methods of fabrication (Robots, as for example in Plato's Columns). In a parallel move between the necessities and desires of the practice and the ambitious studios and seminars in academia, novel toolsets and design concepts are developed to address contemporary architectural problems. These areas can be understood as different territories of interrogation, forming a landscape of opportunities, or as we describe it internally in our office: a design ecology. The interrogation of these distinct territories, and the unique way in which SPAN assembles those various elements to something larger than its parts, is what constitutes part of SPAN's contribution to the discipline. Apart from projects and visual work, SPAN´s contribution to discourse started early with papers to conferences such as IASS (International Association for Shell and Spatial Structures) in 2007, Design Modeling Symposium in 2008, and ACADIA (Association for Computer Aided Design in Architecture) in 2008, which included ideas such as the application of tissue engineering in architecture, aspects of artifact and affect, fabrication, and considerations on architectural details in complex curved geometries. Within the Atlas of Sensations, a second ecology is defined by the contribution to the paradigm shift in the discourse from the continuous to the hyper-articulated surface, which contains an additional level of information. A surface, which describes architectural properties through the deep pochés, folds, joints, niches, and arches it generates.  The question is: How does this shift in the conception of architecture affect the qualities of the design, and by extension the context these objects construct? To further investigate this question the work focuses on one part of the practice's design ecology: design sensibilities. In order to interrogate this question, the presented work observes these moments in SPAN's practice through the lens of geometrical properties. Ultimately resulting in thoughts on Postdigital design ecologies that discuss aspects of design agency in our contemporary age