[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"doc-detail-83292-en":3,"doc-seo-83292-105":29,"detail-sidebar-cat-0-en-105":91},{"code":4,"msg":5,"data":6},0,"success",{"doc_id":7,"user_id":8,"nickname":9,"user_avatar":10,"doc_module":4,"category_id":11,"category_name":12,"doc_title":13,"doc_description":14,"doc_content":15,"file_id":16,"file_url":17,"file_type":18,"file_size":19,"view_count":20,"is_deleted":4,"is_public":20,"is_downloadable":20,"audit_status":20,"page_count":21,"language":22,"language_code":23,"site_id":24,"html_lang":23,"table_of_contents":25,"faqs":26,"seo_title":13,"seo_description":14,"update_tm":27,"read_time":28},83292,1374391974564,"Clementine","https://ap-avatar.wpscdn.com/avatar/14000253aa45c000a9e?x-image-process=image/resize,m_fixed,w_180,h_180&k=1779874745381141002",8,"Research & Report","A Top-Down Deriving Mechanism in Haskell","A Top-Down Deriving Mechanism in Haskell extends Haskell’s class instance deriving machinery to work over composite data types and across multi-level type class hierarchies. The approach eliminates the need to write deriving clauses for every nested data declaration or to manually enumerate all superclasses in a hierarchy. The paper situates the proposal within existing GHC deriving extensions and related techniques such as generalized newtype deriving, deriving via, and Template Haskell-based instance generation, and motivates the reduction of boilerplate in common compiler and AST workloads.","arXiv :2607 .07732v 1 [ cs .PL] 7 Jul 2026  \nA Top-Down Deriving Mechanism in Haskell (draft)  \nSONG ZHANG  \nIn Haskell, class instance deriving and related mechanisms are used pervasively. Their influence extends beyond Haskell: Rust adopts similar ideas in its trait system, and Java libraries such as Lombok use annotations to generate methods such as equals and toString. This paper proposes an extension to Haskell’s existing deriving machinery so that it can operate over composite data types and multi-level type class hierarchies. With this approach, programmers no longer need to write deriving clauses for every data declaration or explicitly enumerate all superclasses in a type class hierarchy.  \nCCS Concepts: • Software and its engineering → Functional languages.  \nAdditional Key Words and Phrases: Haskell, functional programming, generic programming, class instance, anti-pattern  \nACM Reference Format:  \nSong Zhang. 2024. A Top-Down Deriving Mechanism in Haskell (draft). J. ACM 1, 1, Article 1 (September 2024), 13 pages. [https://doi.org/10.1145/1122445.1122456](https://doi.org/10.1145/1122445.1122456)  \n1 Introduction  \n1.1 Background and Related Work  \nHaskell provides several mechanisms for generating class instances automatically. A tool called DrIFT [10] was built as a preprocessor that parses Haskell source code and generates instance declarations. The main Haskell compiler, GHC, provides similar functionality internally for common classes such as Show, Eq, and Ord. Later, GHC introduced language extensions that derive instances for Typeable, Data, Lift, and higher-order classes such as Functor and Foldable.  \nAnother way to declare a type is with the newtype keyword. A newtype must have exactly one constructor with exactly one field, so its runtime representation can be safely coerced[16] to the field type. It is therefore natural to derive a class instance for the wrapper whenever the wrapped field already has that instance. This is the purpose of GeneralizedNewtypeDeriving.  \nWith generic programming in Haskell [2, 3, 5, 6, 11], default type class methods can be defined rather than merely declared by using the DefaultSignatures extension. Combined with DeriveAnyClass, this allows programmers to write either an empty instance or just the class name in a deriving clause after a data type declaration. To resolve ambiguity among these deriving mechanisms, Scott[12][13] introduced three deriving strategies, stock, newtype, and anyclass, into GHC to denote the default mechanism, GeneralizedNewtypeDeriving, and DeriveAnyClass, respectively.  \nMeta-programming with Template Haskell [15] also facilitates class instance generation. Libraries such as aeson provide both generic-programming and meta-programming interfaces for automatic instance generation.  \nAuthor’s Contact Information: Song Zhang, [Haskell.zhang.song@hotmail.com](Haskell.zhang.song@hotmail.com).  \nPermission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires [prior specific permission and/or a fee. Request permissions from permissions@acm.org](prior specific permission and/or a fee. Request permissions from permissions@acm.org).  \n© 2024 ACM.  \nACM 1557-735X/2024/9-ART1  \n[https://doi.org/10.1145/1122445.1122456](https://doi.org/10.1145/1122445.1122456)  \nJ. ACM, Vol. 1, No. 1, Article 1 . Publication date: September 2024 .  \n1:2 Song Zhang  \nMitchell [7] introduced a DSL in the derive1 package for describing boilerplate instance code and using Template Haskell to generate type class instances such as Arbitrary in the QuickCheck package ","cbCaid8NmhUfwaqG","https://ap.wps.com/l/cbCaid8NmhUfwaqG","pdf",580946,1,13,"English","en",105,"# Introduction\n## Background and Related Work\n## Contribution","[{\"question\":\"What problem does the proposed top-down deriving mechanism address?\",\"answer\":\"It addresses boilerplate in Haskell instance deriving by enabling a single deriving declaration to generate multiple related class instances, including for nested composite data types and multi-superclass hierarchies.\"},{\"question\":\"How does the paper’s mechanism improve over existing GHC deriving behavior?\",\"answer\":\"Existing mechanisms mainly generate one class instance for one type at a time. The proposed method automatically generates multiple related instances and can also generate an explicit class context for standalone deriving or instance declarations.\"},{\"question\":\"Which existing Haskell technologies does the paper relate its approach to?\",\"answer\":\"The paper relates to GHC’s built-in deriving capabilities and extensions (including GeneralizedNewtypeDeriving and DeriveAnyClass), generic-programming techniques, and Template Haskell/meta-programming approaches, as well as related mechanisms like deriving via.\"}]",1784186529,33,{"code":4,"msg":30,"data":31},"ok",{"site_id":24,"language":23,"slug":32,"title":13,"keywords":33,"description":14,"schema_data":34,"social_meta":86,"head_meta":88,"extra_data":90,"updated_unix":27},"a-top-down-deriving-mechanism-in-haskell","",{"@graph":35,"@context":85},[36,53,68],{"@type":37,"itemListElement":38},"BreadcrumbList",[39,43,47,50],{"item":40,"name":41,"@type":42,"position":20},"https://docshare.wps.com","Home","ListItem",{"item":44,"name":45,"@type":42,"position":46},"https://docshare.wps.com/document/","Document",2,{"item":48,"name":12,"@type":42,"position":49},"https://docshare.wps.com/document/research-report/",3,{"item":51,"name":13,"@type":42,"position":52},"https://docshare.wps.com/document/a-top-down-deriving-mechanism-in-haskell/83292/",4,{"url":51,"name":13,"@type":54,"author":55,"headline":13,"publisher":57,"fileFormat":60,"inLanguage":23,"description":14,"dateModified":61,"datePublished":62,"encodingFormat":60,"isAccessibleForFree":63,"interactionStatistic":64},"DigitalDocument",{"name":9,"@type":56},"Person",{"url":40,"name":58,"@type":59},"DocShare","Organization","application/pdf","2026-07-17","2026-07-16",true,{"@type":65,"interactionType":66,"userInteractionCount":20},"InteractionCounter",{"@type":67},"ViewAction",{"@type":69,"mainEntity":70},"FAQPage",[71,77,81],{"name":72,"@type":73,"acceptedAnswer":74},"What problem does the proposed top-down deriving mechanism address?","Question",{"text":75,"@type":76},"It addresses boilerplate in Haskell instance deriving by enabling a single deriving declaration to generate multiple related class instances, including for nested composite data types and multi-superclass hierarchies.","Answer",{"name":78,"@type":73,"acceptedAnswer":79},"How does the paper’s mechanism improve over existing GHC deriving behavior?",{"text":80,"@type":76},"Existing mechanisms mainly generate one class instance for one type at a time. The proposed method automatically generates multiple related instances and can also generate an explicit class context for standalone deriving or instance declarations.",{"name":82,"@type":73,"acceptedAnswer":83},"Which existing Haskell technologies does the paper relate its approach to?",{"text":84,"@type":76},"The paper relates to GHC’s built-in deriving capabilities and extensions (including GeneralizedNewtypeDeriving and DeriveAnyClass), generic-programming techniques, and Template Haskell/meta-programming approaches, as well as related mechanisms like deriving via.","https://schema.org",{"og:url":51,"og:type":87,"og:title":13,"og:site_name":58,"og:description":14},"article",{"robots":89,"canonical":51},"index,follow",{"doc_id":7,"site_id":24},{"code":4,"msg":5,"data":92},[93,97,101,105,110,115,120,123,128,131,135],{"id":20,"doc_module":4,"doc_module_name":45,"category_name":94,"show_sort_weight":95,"slug":96},"Story & Novel",90,"story-novel",{"id":46,"doc_module":4,"doc_module_name":45,"category_name":98,"show_sort_weight":99,"slug":100},"Literature",80,"literature",{"id":52,"doc_module":4,"doc_module_name":45,"category_name":102,"show_sort_weight":103,"slug":104},"Exam",70,"exam",{"id":106,"doc_module":4,"doc_module_name":45,"category_name":107,"show_sort_weight":108,"slug":109},5,"Comic",60,"comic",{"id":111,"doc_module":4,"doc_module_name":45,"category_name":112,"show_sort_weight":113,"slug":114},6,"Technology",50,"technology",{"id":116,"doc_module":4,"doc_module_name":45,"category_name":117,"show_sort_weight":118,"slug":119},7,"Healthcare",40,"healthcare",{"id":11,"doc_module":4,"doc_module_name":45,"category_name":12,"show_sort_weight":121,"slug":122},30,"research-report",{"id":124,"doc_module":4,"doc_module_name":45,"category_name":125,"show_sort_weight":126,"slug":127},9,"Religion & Spirituality",20,"religion-spirituality",{"id":126,"doc_module":4,"doc_module_name":45,"category_name":129,"show_sort_weight":126,"slug":130},"World Cup","world-cup",{"id":132,"doc_module":4,"doc_module_name":45,"category_name":133,"show_sort_weight":132,"slug":134},10,"Lifestyle","lifestyle",{"id":136,"doc_module":4,"doc_module_name":45,"category_name":137,"show_sort_weight":106,"slug":138},19,"General","general"]