Programmiersprachen und Rechenkonzepte

Seit 1984 veranstaltet die GI--Fachgruppe "Programmiersprachen und Rechenkonzepte" regelmäßig im Frühjahr einen Workshop im Physikzentrum Bad Honnef. Das Treffen dient in erster Linie dem gegenseitigen Kennenlernen, dem Erfahrungsaustausch, der Diskussion und der Vertiefung gegenseitiger Kontakte

LiquidHaskell : Liquid Types for Haskell

Ακόμα και τα ασφαλή προγράμματα μπορούν να έχουν λάθη. Προγράμματα που έχουν μεταγλωτιστεί με βάση κάποιο ισχυρό σύστημα τύπων, όπως αυτό της Haskell, μπορούν να πετάξουν σφάλμα κατα τον χρόνο εκτέλεσης ή να δώσουν μη αναμενώμενη απάντηση. Τα refinement συστήματα τύπων αντιμετωπίζουν αυτήν την κατάσταση αφού επιτρέπουν την έκφραση σημασιολογικών προδιαφραφών των προγραμμάτων. Αναλύουμε την απόδειξη των προδιαγραφών σε αυτά τα συστήματα. Πολύ εκφραστικά συστήματα απαιτούν ελέγχους κατά τον χρόνο εκτέλεσης ή ρητές αποδείξεις από τον χρήστη, για την αποδειξη των προδιαγραφών, Λιγότερο εκφραστικά συστήματα τύπων επιτρέπουν την αυτόματη απόδειξη των προδιαγραφών, κατά τον χρόνο μεταγλώτισης. Παρουσιάζουμε τους liquidTypes ένα σύστημα τύπων που επιτρέπει την αυτόματη απόδειξη προδιαγραφών κατά τον χρόνο μεταγλώτισης. Επεκτείνουμε τους liquidTypes με abstract refinement, έναν μηχανισμό που αυξάνει την εκφραστικότητα του συστήματος, χωρίς να αυξάνει την πολυπλοκοτητά του. Υλοποιήσαμε την LiquidHaskell ένα σύστημα τύπων για Haskell που συνδιάζει liquidTypes με abstract refinement και το χρησιμοποιήσαμε για να αποδείξουμε ιδιώτητες πραγματικων βιβλιοθηκών της Haskell.Even well-typed programs can go wrong, by returning a wrong answer or throwing a run-time error. A popular response is to allow programmers use refinement type systems to express semantic specifications about programs. We study verification in such systems. On the one hand, expressive refinement type systems require run-time checks or explicit proofs to verify specifications. On the other, less expressive type systems allow static and automatic proofs of the specifications. Next, we present abstract refinement types, a means to enhance the expressiveness of a refinement type system without increasing its complexity. Then, we present LiquidHaskell that combines liquidTypes with abstraction over refinements to enhance expressiveness of LiquidTypes. LiquidHaskell is a quite expressive verification tool for Haskell programs that can be used to check termination, totality and general functional correctness. Finally, we evaluate LiquidHaskell in real world Haskell libraries

A Functional Approach to Hardware Software Co-Design

Developing software for embedded systems presents quite the challenge---not only do these systems demand good knowledge of the hardware they run on, but their limited resources also make it difficult to achieve efficiency. For embedded systems with different kinds of processing elements, the challenge is even greater; the presence of heterogeneous elements both raises all of the issues associated with homogeneous systems, and may also cause non-uniform system development and capability.In this thesis we explore a functional approach to heterogeneous system development, with a staged hardware software co-design language embedded in Haskell, to address many of the modularity problems typically found in such systems. This staged approach enables designers to build their applications from reusable components and skeletons, while retaining control over much of the generated source code. Design exploration also benefits from the functional approach, since Haskell\u27s type classes can be used to ensure that certain operations will be available. As a result, a developer can not only write for hardware and software in the co-design language, but she can also write generic programs that are suitable for both.Internally, the co-design language is based on a monadic representation of imperative programs that abstracts away from its underlying statement, expression, and predicate types by establishing an interface to their respective interpreters. Programs are thus loosely coupled to their underlying types, giving a clear separation of concerns. The compilation process is expressed as a series of translations between progressively smaller typed languages, which safeguards against many common errors.In addition to the hardware software co-design language, this thesis also introduces a language for expressing digital signal processing algorithms, using a model of synchronous data-flow that is embedded in Haskell. The language supports definitions in a functional style, reducing the gap between an algorithm\u27s mathematical specification and its implementation. A vector language is also presented, which builds on a functional representation that guarantees fusion for arrays. Both of these languages are intended to be extensions of the co-design language, but neither one is dependent on it and can thus be used to extend other languages as well

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

Graphical application and visualization of lazy functional computation.

Mere academic toys or the tools of the future? Lazy functional programming languages have undoubted attractive properties. This thesis explores their potential, from the programmer's point of view, for implementing interactive and graphical applications to which they do not seem immediately suited. The discussion is centred round two example applications. One is a graphical design program based on an idea of the artist M. C. Escher. The thesis argues that the graphical user interface may be encapsulated in an "interpret " function that when applied by a mouse click to an interface of appropriate type yields the required behaviour. The second example is a monitoring interpreter for a functional language. The idea is that if the mechanics of the reduction are presented at a suitable level of abstraction, this may be used to give insight into what is going on. On the basis of this the programmer might modify the code so that a program runs more efficiently in terms of speed and memory requirements. Problems of displaying the reduction are addressed, and solutions proposed for overcoming these: displaying the graph as a spanning tree, to ensure planarity, with extra leave

Implementing Functional Logic Programs by Translation into Purely Functional Programs

This work examines a transformation scheme from functional logic programs to purely functional programs both formally and experimentally

Executable Refinement Types

This dissertation introduces executable refinement types, which refine structural types by semi-decidable predicates, and establishes their metatheory and accompanying implementation techniques. These results are useful for undecidable type systems in general. Particular contributions include: (1) Type soundness and a logical relation for extensional equivalence for executable refinement types (though type checking is undecidable); (2) hybrid type checking for executable refinement types, which blends static and dynamic checks in a novel way, in some sense performing better statically than any decidable approximation; (3) a type reconstruction algorithm - reconstruction is decidable even though type checking is not, when suitably redefined to apply to undecidable type systems; (4) a novel use of existential types with dependent types to ensure that the language of logical formulae is closed under type checking (5) a prototype implementation, Sage, of executable refinement types such that all dynamic errors are communicated back to the compiler and are thenceforth static errors.Comment: Ph.D. dissertation. Accepted by the University of California, Santa Cruz, in March 2014. 278 pages (295 including frontmatter