A curation of useful resources for learning about and using recursion schemes.
Recursion schemes are simple, composable combinators, that automate the process of traversing and recursing through nested data structures.
- Practical Recursion Schemes - Introduction to pattern functors, fix points, anamorphisms, catamorphisms, paramorphisms and hylomorphisms, requiring very little prior knowledge.
- An Introduction to Recursion Schemes - Three-part series in which you discover recursion schemes from scratch and implement a small subset of Edward Kmett's library.
- Understanding Algebras - Bartosz Milewski explains F-algebras and shows how to use them in the context of catamorphisms.
- Recursion Schemes: A Field Guide (Redux) - List of various recursion schemes with code samples.
- Catamorphisms - Definition on the Haskell Wiki.
- Catamorphisms - Short definition with code on School of Haskell by Edward Kmett.
- Rotating Squares - Using a hylomorphism to rotate a quadtree by Jared Tobin.
- Promorphisms, Pre and Post - Pratical examples of pre- and postpromorphisms by Jared Tobin.
- Time Traveling Recursion Schemes - Exploring histo and futu by example by Jared Tobin.
- Cheat Sheet - Map of various recursion schemes and their duals.
- Correcting the Visitor pattern - Showing that the Visitor pattern implements an f-algebra for use with a catamorphism (in Java).
- Functional Programming with Bananas, Lenses, Envelopes and Barbed Wire, 1991, Meijer et al. - The original paper most of this is based on.
- A Duality of Sorts, 2013, Hinze et al. - Shows that many basic sorting algorithms exist as a pair, and that these pairs arise naturally out of the duality between folds and unfolds.
- Sorting with Bialgebras and Distributive Laws, 2012, Hinze et al. - Shows how paramorphisms and apomorphisms can be used for more efficient implementations of sorting algorithms.
- Scrap your boilerplate: a practical design pattern for generic programming, 2003, SPJ et al. - Design pattern for writing programs that traverse data structures built from rich mutually-recursive data types.
- Slidedecks by Tim Philip Williams - "Recursion Schemes by Example" and "Exotic Tools for Exotic Trades" provide concise definitions as well as practical examples of many recursion schemes.
- Unifying Structured Recursion Schemes - 12 min presentation by Ralf Hinze, Nicolas Wu, and Jeremy Gibbons.
- Recursion Schemes - Presented by Tim Williams at the London Haskell meetup.
- F-algebras or: How I Learned to Stop Worrying and Love the Type System - Presented by Anthony Burzillo at the NYC Haskell User's Group.
- A Gentle Introduction to Recursion Schemes - Presented by Jean Remi Desjardins at Lambdaconf 2016.
- recursion-scheme-talk - Collection of slide decks about recursion schemes.
- Bracer: Transforming Real-World Languages with Coproducts and Recursion Schemes - High-level talk about structuring programs with coproducts and recursion schemes by Patrick Thomson.
- Recursion: Where Functional Programming Hits Bottom - Introduction to recursive fix point data structures and recursion schemes in Haskell and Scala by Greg Pfeil.
- Programming with algebras - Bartosz Milewski's article in talk form, presented at LambdaCon.
- Magic Read Along - Casual discussions about category theory that often bring up recursion schemes, including episode 33 which talks about Histomorphisms and Futumorphisms.
- recursion-schemes for Haskell - The canonical implementation by Edward Kmett.
- Matryoshka for Scala - Generalized folds, unfolds, and traversals for fixed point data structures.
- purescript-matryoshka for PureScript - Work-in-process port of matryoshka.
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