31 research outputs found
Squid: Type-Safe, Hygienic, and Reusable Quasiquotes
Quasiquotes have been shown to greatly simplify the task of metaprogramming. This is in part because they hide the data structures of the intermediate representation (IR), instead allowing metaprogrammers to use the concrete syntax of the language they manipulate. Scala has had ``syntactic'' quasiquotes for a long time, but still misses a statically-typed version like in MetaOCaml, Haskell and F#. This safer flavor of quasiquotes has been particularly useful for staging and domain-specific languages. In this paper we present Squid, a metaprogramming system for Scala that fills this gap. Squid quasiquotes are novel in three ways: they are the first statically-typed quasiquotes we know that allow code inspection (via pattern matching); they are implemented purely as a macro library, without modifications to the compiler; and they are reusable in the sense that they can manipulate different IRs. Adapting (or binding) a new IR to Squid is done simply by implementing a well-defined interface in the style of object algebras (i.e., tagless-final). We detail how Squid is implemented, leveraging the metaprogramming tools already offered by Scala, and show three application examples: the definition of a binding for a DSL in the style of LMS; a safe ANF conversion; and the introduction of type-safe, hygienic macros as an alternative to the current macro system
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A Tool for Producing Verified, Explainable Proofs
Mathematicians are reluctant to use interactive theorem provers. In this thesis I argue that this is because proof assistants don't emphasise explanations of proofs; and that in order to produce good explanations, the system must create proofs in a manner that mimics how humans would create proofs. My research goals are to determine what constitutes a human-like proof and to represent human-like reasoning within an interactive theorem prover to create formalised, understandable proofs. Another goal is to produce a framework to visualise the goal states of this system.
To demonstrate this, I present HumanProof: a piece of software built for the Lean 3 theorem prover. It is used for interactively creating proofs that resemble how human mathematicians reason. The system provides a visual, hierarchical representation of the goal and a system for suggesting available inference rules. The system produces output in the form of both natural language and formal proof terms which are checked by Lean's kernel. This is made possible with the use of a structured goal state system which interfaces with Lean's tactic system which is detailed in Chapter 3.
In Chapter 4, I present the subtasks automation planning subsystem, which is used to produce equality proofs in a human-like fashion. The basic strategy of the subtasks system is break a given equality problem in to a hierarchy of tasks and then maintain a stack of these tasks in order to determine the order in which to apply equational rewriting moves. This process produces equality chains for simple problems without having to resort to brute force or specialised procedures such as normalisation. This makes proofs more human-like by breaking the problem into a hierarchical set of tasks in the same way that a human would.
To produce the interface for this software, I also created the ProofWidgets system for Lean 3. This system is detailed in Chapter 5. The ProofWidgets system uses Lean's metaprogramming framework to allow users to write their own interactive, web-based user interfaces to display within the VSCode editor and in an online web-editor. The entire tactic state is available to the rendering engine, and hence expression structure and types of subexpressions can be explored interactively. The ProofWidgets system also allows the user interface to interactively edit the proof document, enabling a truly interactive modality for creating proofs; human-like or not.
In Chapter 6, the system is evaluated by asking real mathematicians about the output of the system, and what it means for a proof to be understandable to them. The user group study asks participants to rank and comment on proofs created by HumanProof alongside natural language and pure Lean proofs. The study finds that participants generally prefer the HumanProof format over the Lean format. The verbal responses collected during the study indicate that providing intuition and signposting are the most important properties of a proof that aid understanding.EPSR
Extensible Languages for Flexible and Principled Domain Abstraction
Die meisten Programmiersprachen werden als Universalsprachen entworfen. UnabhĂ€ngig von der zu entwickelnden Anwendung, stellen sie die gleichen Sprachfeatures und Sprachkonstrukte zur VerfĂŒgung. Solch universelle Sprachfeatures ignorieren jedoch die spezifischen Anforderungen, die viele Softwareprojekte mit sich bringen.
Als Gegenkraft zu Universalsprachen fördern domÀnenspezifische Programmiersprachen, modellgetriebene Softwareentwicklung und sprachorientierte Programmierung die Verwendung von DomÀnenabstraktion, welche den Einsatz von domÀnenspezifischen Sprachfeatures und Sprachkonstrukten ermöglicht. Insbesondere erlaubt DomÀnenabstraktion Programmieren auf dem selben Abstraktionsniveau zu programmieren wie zu denken und vermeidet dadurch die Notwendigkeit DomÀnenkonzepte mit universalsprachlichen Features zu kodieren.
Leider ermöglichen aktuelle AnsĂ€tze zur DomĂ€nenabstraktion nicht die Entfaltung ihres ganzen Potentials. Einerseits mangelt es den AnsĂ€tzen fĂŒr interne domĂ€nenspezifische Sprachen an FlexibilitĂ€t bezĂŒglich der Syntax, statischer Analysen, und WerkzeugunterstĂŒtzung, was das tatsĂ€chlich erreichte Abstraktionsniveau beschrĂ€nkt. Andererseits mangelt es den AnsĂ€tzen fĂŒr externe domĂ€nenspezifische Sprachen an wichtigen Prinzipien, wie beispielsweise modularem SchlieĂen oder Komposition von DomĂ€nenabstraktionen, was die Anwendbarkeit dieser AnsĂ€tze in der Entwicklung gröĂerer Softwaresysteme einschrĂ€nkt. Wir verfolgen in der vorliegenden Doktorarbeit einen neuartigen Ansatz, welcher die Vorteile von internen und externen domĂ€nenspezifischen Sprachen vereint um flexible und prinzipientreue DomĂ€nenabstraktion zu unterstĂŒtzen.
Wir schlagen bibliotheksbasierte erweiterbare Programmiersprachen als Grundlage fĂŒr DomĂ€nenabstraktion vor. In einer erweiterbaren Sprache kann DomĂ€nenabstraktion durch die Erweiterung der Sprache mit domĂ€nenspezifischer Syntax, statischer Analyse, und WerkzeugunterstĂŒtzung erreicht werden . Dies ermöglicht DomĂ€nenabstraktionen die selbe FlexibilitĂ€t wie externe domĂ€nenspezifische Sprachen. Um die Einhaltung ĂŒblicher Prinzipien zu gewĂ€hrleisten, organisieren wir Spracherweiterungen als Bibliotheken und verwenden einfache Import-Anweisungen zur Aktivierung von Erweiterungen. Dies erlaubt modulares SchlieĂen (durch die Inspektion der Import-Anweisungen), unterstĂŒtzt die Komposition von DomĂ€nenabstraktionen (durch das Importieren mehrerer Erweiterungen), und ermöglicht die uniforme Selbstanwendbarkeit von Spracherweiterungen in der Entwicklung zukĂŒnftiger Erweiterungen (durch das Importieren von Erweiterungen in einer Erweiterungsdefinition). Die Organisation von Erweiterungen in Form von Bibliotheken ermöglicht DomĂ€nenabstraktionen die selbe Prinzipientreue wie interne domĂ€nenspezifische Sprachen.
Wir haben die bibliotheksbasierte erweiterbare Programmiersprache SugarJ entworfen und implementiert. SugarJ Bibliotheken können Erweiterungen der Syntax, der statischen Analyse, und der WerkzeugunterstĂŒtzung von SugarJ deklarieren. Eine syntaktische Erweiterung besteht dabei aus einer erweiterten Syntax und einer Transformation der erweiterten Syntax in die Basissyntax von SugarJ. Eine Erweiterung der Analyse testet Teile des abstrakten Syntaxbaums der aktuellen Datei und produziert eine Liste von Fehlern. Eine Erweiterung der WerkzeugunterstĂŒtzung deklariert Dienste wie SyntaxfĂ€rbung oder CodevervollstĂ€ndigung fĂŒr bestimmte Sprachkonstrukte. SugarJ Erweiterungen sind vollkommen selbstanwendbar: Eine erweiterte Syntax kann in eine Erweiterungsdefinition transformiert werden, eine erweiterte Analyse kann Erweiterungsdefinitionen testen, und eine erweiterte WerkzeugunterstĂŒtzung kann Entwicklern beim Definieren von Erweiterungen assistieren. Um eine Quelldatei mit Erweiterungen zu verarbeiten, inspizieren der SugarJ Compiler und die SugarJ IDE die importierten Bibliotheken um die aktiven Erweiterungen zu bestimmen. Der Compiler und die IDE adaptieren den Parser, den Codegenerator, die Analyseroutine und die WerkzeugunterstĂŒtzung der Quelldatei entsprechend der aktiven Erweiterungen.
Wir beschreiben in der vorliegenden Doktorarbeit nicht nur das Design und die Implementierung von SugarJ, sondern berichten darĂŒber hinaus ĂŒber Erweiterungen unseres ursprĂŒnglich Designs. Insbesondere haben wir eine Generalisierung des SugarJ Compilers entworfen und implementiert, die neben Java alternative Basissprachen unterstĂŒtzt. Wir haben diese Generalisierung verwendet um die bibliotheksbasierten erweiterbaren Programmiersprachen SugarHaskell, SugarProlog, und SugarFomega zu entwickeln. Weiterhin haben wir SugarJ ergĂ€nzt um polymorphe DomĂ€nenabstraktion und KommunikationsintegritĂ€t zu unterstĂŒtzen. Polymorphe DomĂ€nenabstraktion ermöglicht Programmierern mehrere Transformationen fĂŒr die selbe domĂ€nenspezifische Syntax bereitzustellen. Dies erhöht die FlexibilitĂ€t von SugarJ und unterstĂŒtzt bekannte Szenarien aus der modellgetriebenen Entwicklung. KommunikationsintegritĂ€t spezifiziert, dass die Komponenten eines Softwaresystems nur ĂŒber explizite KanĂ€le kommunizieren dĂŒrfen. Im Kontext von Codegenerierung stellt dies eine interessante Eigenschaft dar, welche die Generierung von impliziten ModulabhĂ€ngigkeiten untersagt. Wir haben KommunikationsintegritĂ€t als weiteres Prinzip zu SugarJ hinzugefĂŒgt.
Basierend auf SugarJ und zahlreicher Fallstudien argumentieren wir, dass flexible und prinzipientreue DomĂ€nenabstraktion ein skalierbares Programmiermodell fĂŒr die Entwicklung komplexer Softwaresysteme darstellt
Scoped and Typed Staging by Evaluation
Using a dependently typed host language, we give a well scoped-and-typed by
construction presentation of a minimal two level simply typed calculus with a
static and a dynamic stage. The staging function partially evaluating the part
of a term that are static is obtained by a model construction inspired by
normalisation by evaluation.
We then go on to demonstrate how this minimal language can be extended to
provide additional metaprogramming capabilities, and to define a higher order
functional language evaluating to digital circuit descriptions.Comment: As accepted for publication at PEPM 202
Finally, a Polymorphic Linear Algebra Language (Pearl)
Many different data analytics tasks boil down to linear algebra primitives. In practice, for each different type of workload, data scientists use a particular specialised library. In this paper, we present Pilatus, a polymorphic iterative linear algebra language, applicable to various types of data analytics workloads. The design of this domain-specific language (DSL) is inspired by both mathematics and programming languages: its basic constructs are borrowed from abstract algebra, whereas the key technology behind its polymorphic design uses the tagless final approach (a.k.a. polymorphic embedding/object algebras). This design enables us to change the behaviour of arithmetic operations to express matrix algebra, graph algorithms, logical probabilistic programs, and differentiable programs. Crucially, the polymorphic design of Pilatus allows us to use multi-stage programming and rewrite-based optimisation to recover the performance of specialised code, supporting fixed sized matrices, algebraic optimisations, and fusion
Scoped and typed staging by evaluation
Using a dependently typed host language, we give a well scoped-and-typed by construction presentation of a minimal two level simply typed calculus with a static and a dynamic stage. The staging function partially evaluating the parts of a term that are static is obtained by a model construction inspired by normalisation by evaluation. We then go on to demonstrate how this minimal language can be extended to provide additional metaprogramming capabilities, and to define a higher order functional language evaluating to digital circuit descriptions
On the Expressive Power of User-Defined Effects: Effect Handlers, Monadic Reflection, Delimited Control
We compare the expressive power of three programming abstractions for
user-defined computational effects: Bauer and Pretnar's effect handlers,
Filinski's monadic reflection, and delimited control without
answer-type-modification. This comparison allows a precise discussion about the
relative expressiveness of each programming abstraction. It also demonstrates
the sensitivity of the relative expressiveness of user-defined effects to
seemingly orthogonal language features. We present three calculi, one per
abstraction, extending Levy's call-by-push-value. For each calculus, we present
syntax, operational semantics, a natural type-and-effect system, and, for
effect handlers and monadic reflection, a set-theoretic denotational semantics.
We establish their basic meta-theoretic properties: safety, termination, and,
where applicable, soundness and adequacy. Using Felleisen's notion of a macro
translation, we show that these abstractions can macro-express each other, and
show which translations preserve typeability. We use the adequate finitary
set-theoretic denotational semantics for the monadic calculus to show that
effect handlers cannot be macro-expressed while preserving typeability either
by monadic reflection or by delimited control. We supplement our development
with a mechanised Abella formalisation
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Extending old languages for new architectures
Architectures evolve quickly. The number of transistors available to chip designers doubles every 18 months, allowing
increasingly complex architectures to be developed on a single chip. Power dissipation issues have forced chip designers
to look for new ways to use the transistors at their disposal. This situation inevitably leads to new architectural
features on a fairly regular basis. Enabling programmers to benefit from these new architectural features can be
problematic.
Since architectures change frequently, and compilers last for a long time, it is clear that compilers should be designed
to be extensible. This thesis argues that to support evolving architectures a compiler should support the creation of
high-level language extensions. In particular, it must support extending the compiler's middle-end. We describe the
design of EMCC, a C compiler that allows extension of its front-, middle- and back-ends.
OpenMP is an extension to the C programming language to support parallelism. It has recently added support for
task-based parallelism, a dynamic form of parallelism made popular by Cilk. However, implementing task-based parallelism
efficiently requires much more involved program transformation than the simple static parallelism originally supported
by OpenMP. We use EMCC to create an implementation of OpenMP, with particular focus on efficient implementation of
task-based parallelism.
We also demonstrate the benefits of supporting high-level analysis through an extended middle-end, by developing and
implementing an interprocedural analysis that improves the performance of task-based parallelism by allowing tasks to
share stacks. We develop a novel generalisation of logic programming that we use to concisely express this analysis, and
use this formalism to demonstrate that the analysis can be executed in polynomial time.
Finally, we design extensions to OpenMP to support heterogeneous architectures