2 Search Results for "Karachalias, Georgios"

Document
DOI: 10.4230/LIPIcs.ECOOP.2025.2
The Algebra of Patterns

Authors: David Binder and Lean Ermantraut

Published in: LIPIcs, Volume 333, 39th European Conference on Object-Oriented Programming (ECOOP 2025)

Abstract
Pattern matching is a popular feature in functional, imperative and object-oriented programming languages. Language designers should therefore invest effort in a good design for pattern matching. Most languages choose a first-match semantics for pattern matching; that is, clauses are tried in the order in which they appear in the program until the first one matches. As a consequence, the order in which the clauses appear cannot be arbitrarily changed, which results in a less declarative programming model. The declarative alternative to this is an order-independent semantics for pattern matching, which is not implemented in most programming languages since it requires more verbose patterns. The reason for this verbosity is that the syntax of patterns is usually not expressive enough to express the complement of a pattern. In this paper, we show a principled way to make order-independent pattern matching practical. Our solution consists of two parts: First, we introduce a boolean algebra of patterns which can express the complement of a pattern. Second, we introduce default clauses to pattern matches. These default clauses capture the essential idea of a fallthrough case without sacrificing the property of order-independence.
Cite as

David Binder and Lean Ermantraut. The Algebra of Patterns. In 39th European Conference on Object-Oriented Programming (ECOOP 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 333, pp. 2:1-2:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{binder_et_al:LIPIcs.ECOOP.2025.2,
  author =	{Binder, David and Ermantraut, Lean},
  title =	{{The Algebra of Patterns}},
  booktitle =	{39th European Conference on Object-Oriented Programming (ECOOP 2025)},
  pages =	{2:1--2:28},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-373-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{333},
  editor =	{Aldrich, Jonathan and Silva, Alexandra},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2025.2},
  URN =		{urn:nbn:de:0030-drops-232959},
  doi =		{10.4230/LIPIcs.ECOOP.2025.2},
  annote =	{Keywords: functional programming, pattern matching, algebraic data types, equational reasoning}
}
Document
DOI: 10.4230/LIPIcs.ITP.2023.8
No Unification Variable Left Behind: Fully Grounding Type Inference for the HDM System

Authors: Roger Bosman, Georgios Karachalias, and Tom Schrijvers

Published in: LIPIcs, Volume 268, 14th International Conference on Interactive Theorem Proving (ITP 2023)

Abstract
The Hindley-Damas-Milner (HDM) system provides polymorphism, a key feature of functional programming languages such as Haskell and OCaml. It does so through a type inference algorithm, whose soundness and completeness have been well-studied and proven both manually (on paper) and mechanically (in a proof assistant). Earlier research has focused on the problem of inferring the type of a top-level expression. Yet, in practice, we also may wish to infer the type of subexpressions, either for the sake of elaboration into an explicitly-typed target language, or for reporting those types back to the programmer. One key difference between these two problems is the treatment of underconstrained types: in the former, unification variables that do not affect the overall type need not be instantiated. However, in the latter, instantiating all unification variables is essential, because unification variables are internal to the algorithm and should not leak into the output. We present an algorithm for the HDM system that explicitly tracks the scope of all unification variables. In addition to solving the subexpression type reconstruction problem described above, it can be used as a basis for elaboration algorithms, including those that implement elaboration-based features such as type classes. The algorithm implements input and output contexts, as well as the novel concept of full contexts, which significantly simplifies the state-passing of traditional algorithms. The algorithm has been formalised and proven sound and complete using the Coq proof assistant.
Cite as

Roger Bosman, Georgios Karachalias, and Tom Schrijvers. No Unification Variable Left Behind: Fully Grounding Type Inference for the HDM System. In 14th International Conference on Interactive Theorem Proving (ITP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 268, pp. 8:1-8:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

Copy BibTex To Clipboard

@InProceedings{bosman_et_al:LIPIcs.ITP.2023.8,
  author =	{Bosman, Roger and Karachalias, Georgios and Schrijvers, Tom},
  title =	{{No Unification Variable Left Behind: Fully Grounding Type Inference for the HDM System}},
  booktitle =	{14th International Conference on Interactive Theorem Proving (ITP 2023)},
  pages =	{8:1--8:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-284-6},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{268},
  editor =	{Naumowicz, Adam and Thiemann, Ren\'{e}},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2023.8},
  URN =		{urn:nbn:de:0030-drops-183836},
  doi =		{10.4230/LIPIcs.ITP.2023.8},
  annote =	{Keywords: type inference, mechanization, let-polymorphism}
}
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