RepLib: A library for derivable type classes

Some type class instances can be automatically derived from the structure of types. As a result, the Haskell language includes the deriving mechanism to automatic generates such instances for a small number of built-in type classes. In this paper, we present RepLib, a GHC library that enables a similar mechanism for arbitrary type classes. Users of RepLib can define the relationship between the structure of a datatype and the associated instance declaration by a normal Haskell functions that pattern-matches a representation types. Furthermore, operations defined in this manner are extensible-instances for specific types not defined by type structure may also be incorporated. Finally, this library also supports the definition of operations defined by parameterized types

Produktiivsema Java EE ökosüsteemi poole

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Alates Java programmeerimiskeele loomisest 1995. a. on selle üks kõige olulisemaid kasutusvaldkondi veebirakenduste programmeerimine. Java populaarsuse põhjuseks ei olnud ainult keeledisainilised omadused nagu objektorienteeritus ja range tüübisüsteem, vaid ennekõike platvormist sõltumatus ja standardiseeritud teekide rohkus, mis tegi tavaprogrammeerijatele veebirakenduste programmeerimise jõukohaseks. Kümme aastat hiljem oli olukord muutunud märkimisväärselt. Java oli kaotamas oma liidripositsiooni uutele, nn. dünaamilistele keeltele nagu PHP, Ruby ja Python. Seejuures polnud põhjuseks mitte see, et need keeled ise oleksid tunduvalt Javast paremad, vaid Java ökosüsteemi areng oli väga konservatiivne ja aeglane. Antud kontekstis alustasime aastal 2005 oma uuringuid eesmärgiga parandada suurimad probleemid Java ökosüsteemis ja viia see vähemalt samale tasemele ülalmainitud keeltega. Käesaolevas dissertatsioonis on esitatud vastavate uuringute tulemused. Dissertatsioon põhineb neljal publikatsioonil—kolmel eelretsenseeritud teadusartiklil ja ühel patendil. Esimeseks katseks oli uue veebiraamistike integreerimisraamistiku “Aranea” loomine. Antud hetkel oli Javas üle kolmekümne aktiivselt arendatavat veebiraamistikku, mistõttu otsustasime fokuseeruda kahele võtmeprobleemile: raamistike taaskasutatavuse lihtsus ja koostöövõime. Selleks töötasime välja uudse komponentmudeli, mis võimaldab kirjeldada süsteemi teenus- ja kasutajaliideskomponentide hierarhilisi seoseid, ja realiseerisime eri raamistike adapterid komponentmudelisse sobitumiseks. Järgmise probleemina käsitlesime andmete haldamiskihi kirjeldamist. Lähtusime eeldusest, et relatsioonilistes andmebaasides on SQL kõige enamlevinud andmete kirjelduskeel, ja efektiivne admehalduskiht peab võimaldama Javas lihtsasti esitada SQL päringuid, samas garanteerima konstrueeritavate päringute süntaktilise korrektsuse. Senised lahendused baseerusid reeglina SQL päringute programsel konstrueerimisel sõnedena, mistõttu päringute korrektsuse kontroll oli raskendatud. Lahenduseks töötasime välja nn. rakendispetsiifilise keele (i.k. domain-specific language, DSL) SQL päringute esitamiseks kasutades Java keele tüübisüsteemi vahendeid nende korrektsuse kompileerimisaegseks valideerimiseks. Töö käigus identifitseerisime üldised tarkvara disainimustrid, mis lihtsustavad analoogiliste tüübikindlate DSLide loomist, ja kasutasime neid kahe uue eksperimentaalse tüübikindla DSLi loomisel - Java klasside täitmisaegseks loomiseks ja manipuleerimiseks ning XMLi parsimiseks ja genereerimiseks. Kolmanda ülesandena pühendusime ühele olulisemale Java platvormi puudusele võrreldes dünaamiliste keeltega. Kui PHP’s või Ruby’s saab programmi koodi otseselt muuta ja tulemust koheselt näha, siis Java rakendusserverid nõuavad rakenduse “ehitamist” (i.k. build) ja “paigutamist” (i.k. deploy), mis suurte rakenduste korral võib võtta mitmeid või isegi kümneid minuteid. Probleemi lahenduseks töötasime välja uudse ja praktilise meetodi koodi ümberlaadimiseks Java platvormil, mille põhjal arendasime ja lasime välja toote “JRebel”. See kasutab Java baitkoodi laadimisaegset modifitseerimist koos spetsiaalse ümbersuunamiskihiga kutsekohtade, meetodite ja meetodikeha vahel, mis võimaldab hallata koodi erinevaid versioone ning täitmisajal suunata väljakutsed viimasele versioonile. Täna, rohkem kui seitse aastat pärast uuringute algust, tuleb tõdeda, et meie töö veebiraamistikega lõi küll eduka platvormi erinevate eksperimentaalsete ideede uurimiseks ja katsetamiseks, kuid reaalses tarkvaratööstuses ei ole leidnud laialdast kasutust. Töö tüübikindlate DSLidega oli edukam, sest see mõjutas otseselt edaspidiseid uuringuid antud teemal ning selle elemendid leidsid rakendust viimases JPA standardi spetsifikatsioonis. Kõige suurem mõju tarkvaratööstusele on meie dünaamiline koodiümberlaadimise lahendus, mis on tänapäeval Java kogukonnas laialdaselt kasutusel ning mida kasutavad igapäevaselt rohkem kui 3000 erinevat organisatsiooni üle maailma.Since the Tim Berners-Lee famous proposal of World Wide Web in 1990 and the introduction of the Common Gateway Interface in 1993, the world of online web applications has been booming. In the nineties the Java language and platform became the first choice for web development in and out of the enterprise. But by the mid-aughts the platform was in crisis - newcomers like PHP, Ruby and Python have picked up the flag as the most productive platforms, with Java left for conservative enterprises. However, this was not because those languages and platforms were significantly better than Java. Rather, the issue was that innovation in the Java ecosystem was slow, due to the ways the platform was managed. Large vendors dominated the space, committees designed standards and the brightest minds were moving to other JVM languages like Scala, Groovy or JRuby. In this context we started our investigations in 2005. Our goals were to address some of the more gaping holes in the Java ecosystem and bring it on par with the languages touted as more productive. The first effort was to design a better web framework, called “Aranea”. At that point of time Java had more than thirty actively developed web frameworks, and many of them were used simultaneously in the same projects. We decided to focus on two key issues: ease of reuse and framework interoperability. To solve the first issue we created a self-contained component model that allowed the construction of both simple and sophisticated systems using a simple object protocol and hierarchical aggregation in style of the Composite design pattern. This allowed one to capture every aspect of reuse in a dedicated component, be it a part of framework functionality, a repeating UI component or a whole UI process backed by complex logic. Those could be mixed and matched almost indiscriminately subject to rules expressed in the interfaces they implemented. To solve the second issue we proposed adapters between the component model and the various models of other frameworks. We later implemented some of those adapters both in a local and remote fashion, allowing one to almost effortlessly capture and mix different web application components together, no matter what the underlying implementation may be. The next issue that we focused on was the data access layer. At that point in the Java community the most popular ways of accessing data was either using embedded SQL strings or an Object-Relational Mapping tool ``Hibernate''. Both approaches had severe disadvantages. Using embedded SQL strings exposed the developers to typographical errors, lack of abstraction, very late validation and dangers of dynamic string concatenation. Using Hibernate/ORM introduced a layer of abstraction notorious for the level of misunderstanding and production performance issues it caused. We believed that SQL is the right way to access the data in a relational database, as it expresses exactly the data that is needed without much overhead. Instead of embedding it into strings, we decided to embed it using the constructs of the Java language, thus creating an embedded DSL. As one of the goals was to provide extensive compiler-time validation, we made extensive use of Java Generics and code generation to provide maximum possible static safety. We also built some basic SQL extensions into the language that provided a better interface between Java structures and relational queries as well as allowing effortless further extension and enabling ease of abstraction. Our work on the SQL DSL made us believe that building type safe embedded DSLs could be of great use for the Java community. We embarked on building two more experimental DSLs, one for generating and manipulating Java classes on-the-fly and the other for parsing and generating XML. These experiments exposed some common patterns, including restricting DSL syntax, collecting type safe history and using type safe metadata. Applying those patterns to different domains helps encode a truly type safe DSL in the Java language. Our final and largest effort concentrated on a major disadvantage of the Java platform as compared to the dynamically-typed language platforms. Namely, while in PHP or Ruby on Rails one could edit any line of code and see the result immediately, the Java application servers would force one to do “build” and “deploy”, which for larger applications could take minutes and even tens of minutes. Initial investigation revealed that the claims of fast code reloading were not quite solid across the board. Dynamically-typed languages would typically destroy state and recreate the application, just like the Java application servers. The crucial difference was that they did it quickly and the productivity of development was a large concern for language and framework designers. However as we investigated the issue deeper on the Java side, we came up with a novel and practical way of reloading code on the JVM, which we developed and released as the product “JRebel”. We made use of the fact that Java bytecode is a very high level encoding of the Java language, which is easy to modify during load time. This allowed us to insert a layer of indirection between the call sites, methods and method bodies which was versatile enough to manage multiple versions of code and redirect the calls to the latest version during runtime. There have been over the years some basic developments in the similar fashion, but unlike them we engineered JRebel to run on the stock JVM and to have no visible impact on application functional or non-functional behaviour. The latter was the hardest, as the layer of indirection both introduces numerous compatibility problems and adds performance overhead. To overcome those limitations we had to integrate deeply on many levels of the JVM and to use compiler techniques to remove the layer of indirection where possible

Refunctionalization at Work

We present the left inverse of Reynolds's defunctionalization and we show its relevance to programming and to programming languages. We present two methods to put a program that is almost in defunctionalized form into one that is actually in defunctionalized form, and we illustrate them with a recognizer for Dyck words and with Dijkstra's shunting-yard algorithm

On One-Pass CPS Transformations

We bridge two distinct approaches to one-pass CPS transformations, i.e., CPS transformations that reduce administrative redexes at transformation time instead of in a post-processing phase. One approach is compositional and higher-order, and is independently due to Appel, Danvy and Filinski, and Wand, building on Plotkin's seminal work. The other is non-compositional and based on a reduction semantics for the lambda-calculus, and is due to Sabry and Felleisen. To relate the two approaches, we use three tools: Reynolds's defunctionalization and its left inverse, refunctionalization; a special case of fold-unfold fusion due to Ohori and Sasano, fixed-point promotion; and an implementation technique for reduction semantics due to Danvy and Nielsen, refocusing. This work is directly applicable to transforming programs into monadic normal form

Refunctionalization at Work

We present the left inverse of Reynolds's defunctionalization and we show its relevance to programming and to programming languages. We propose two methods to transform a program that is almost in defunctionalized form into one that is actually in defunctionalized form, and we illustrate them with a recognizer for Dyck words and with Dijkstra's shunting-yard algorithm

Verified Self-Explaining Computation

Common programming tools, like compilers, debuggers, and IDEs, crucially rely on the ability to analyse program code to reason about its behaviour and properties. There has been a great deal of work on verifying compilers and static analyses, but far less on verifying dynamic analyses such as program slicing. Recently, a new mathematical framework for slicing was introduced in which forward and backward slicing are dual in the sense that they constitute a Galois connection. This paper formalises forward and backward dynamic slicing algorithms for a simple imperative programming language, and formally verifies their duality using the Coq proof assistant

UTP, Circus, and Isabelle

We dedicate this paper with great respect and friendship to He Jifeng on the occasion of his 80th birthday. Our research group owes much to him. The authors have over 150 publications on unifying theories of programming (UTP), a research topic Jifeng created with Tony Hoare. Our objective is to recount the history of Circus (a combination of Z, CSP, Dijkstra’s guarded command language, and Morgan’s refinement calculus) and the development of Isabelle/UTP. Our paper is in two parts. (1) We first discuss the activities needed to model systems: we need to formalise data models and their behaviours. We survey our work on these two aspects in the context of Circus. (2) Secondly, we describe our practical implementation of UTP in Isabelle/HOL. Mechanising UTP theories is the basis of novel verification tools. We also discuss ongoing and future work related to (1) and (2). Many colleagues have contributed to these works, and we acknowledge their support

An Analytical Approach to Programs as Data Objects

This essay accompanies a selection of 32 articles (referred to in bold face in the text and marginally marked in the bibliographic references) submitted to Aarhus University towards a Doctor Scientiarum degree in Computer Science.The author's previous academic degree, beyond a doctoral degree in June 1986, is an "Habilitation à diriger les recherches" from the Université Pierre et Marie Curie (Paris VI) in France; the corresponding material was submitted in September 1992 and the degree was obtained in January 1993.The present 32 articles have all been written since 1993 and while at DAIMI.Except for one other PhD student, all co-authors are or have been the author's students here in Aarhus

Piesārņotu grunšu un augšņu rekultivācija ar modificētām piedevām - smago metālu imobilizācija

Elektroniskā versija nesatur pielikumusPiesārņojums ar smagajiem metāliem augsnē ir nopietna vides problēma. Bijušajās rūpnieciskajās, izgāztuvju, militārajās teritorijās atstātais vēsturiskais augsnes piesārņojums un tā rekultivācija ir jautājums, kura risināšanai iespējami dažādi varianti. Promocijas darbā “Piesārņotu grunšu un augšņu rekultivācija ar modificētām piedevām – smago metālu imobilizācija” tika veikti eksperimentāli pētījumi par inovatīvu modificētu piedevu – modificēta māla un humusvielu – izmantošanu efektīvai smago metālu piesārņojuma imobilizācijai. Papildus tika izvērtētas metālu atrašanās formas piesārņotajās un rekultivētajās augsnēs, kā arī inovatīvo augsnes sorbentu efektivitāte. Papildus izstrādāti ieteikumi pamatotai atbilstošo modificēto piedevu izvēlei kompleksa piesārņojuma gadījumos. Pētījumu rezultāti liecina, ka modificētajām piedevām, kas iegūtas no lokālām izejvielām, ir labas perspektīvas, lai videi draudzīgi rekultivētu ar smagajiem metāliem piesārņotu substrātu; piedāvāts indikatīvais modelis piemērotu rekultivācijas tehnoloģiju izvēles pamatojuma izstrādes vajadzībām. Atslēgvārdi: smagie metāli, “vieglā” rekultivācija, stabilizācija/-Heavy metal contamination is the inheritance of modern society and a serious environmental problem. Brownfields, dump sites, former and active industrial and military areas often demand remedial solutions concerning this problem. The aim of the dissertation “Contamination remediation with soil amendments by immobilization of heavy metals” included the development and testing of applicable soil amendments for hard and gentle heavy metal remediation approaches and the elaboration of an indicative decision support model for choosing the best available solution. In addition, aspects of metal speciation and immobilization efficiency were studied through experimental work with innovative modified clay and humic substances as remedial soil amendments. The obtained results revealed broad perspectives for the use of local resources in gentle remediation by soil amendments for heavy metal contaminated territories and showed indicative guidelines on how to choose the right applicable method in different cases