DOI

Type classes are one of Haskell's most popular features and extend its type system with ad-hoc polymorphism. Since their conception, there were useful features that could not be offered because of the desire to offer two correctness properties: coherence and global uniqueness of instances. Coherence essentially guarantees that program semantics are independent from type-checker internals. Global uniqueness of instances is relied upon by libraries for enforcing, for example, that a single order relation is used for all manipulations of an ordered binary tree. The features that could not be offered include explicit dictionary application and local instances, which would be highly useful in practice. In this paper, we propose a new design for offering explicit dictionary application, without compromising coherence and global uniqueness. We introduce a novel criterion based on GHC's type argument roles to decide when a dictionary application is safe with respect to global uniqueness of instances. We preserve coherence by detecting potential sources of incoherence, and prove it formally. Moreover, our solution makes it possible to use local dictionaries. In addition to developing our ideas formally, we have implemented a working prototype in GHC.

Original languageEnglish
Title of host publicationHaskell 2018 - Proceedings of the 11th ACM SIGPLAN International Symposium on Haskell, co-located with ICFP 2018
PublisherAssociation for Computing Machinery, Inc
Pages81-93
Number of pages13
ISBN (Electronic)9781450358354
DOIs
Publication statusPublished - 17 Sep 2018
Event11th ACM SIGPLAN International Symposium on Haskell, Haskell 2018, co-located with ICFP 2018 - St. Louis, United States
Duration: 27 Sep 201828 Sep 2018

Conference

Conference11th ACM SIGPLAN International Symposium on Haskell, Haskell 2018, co-located with ICFP 2018
CountryUnited States
CitySt. Louis
Period27/09/1828/09/18

    Research areas

  • Coherence, Dictionaries, Haskell, Type classes

ID: 40454182