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Catamorphism, anamorphism, hylopmorphism, as opposed to something like fold/unfold, foldAndUnfold. There are of course, many more[1]. Meijer et al just chose a

• bcherny 9y ago
  These are just combinators [1] with long names, right? [1] https://www.npmjs.com/package/combinators-js https://www.npmjs.com/package/combinators-js
  • Tarean 9y ago
    Nope. Example of recursion schemes: You have a binary tree data Tree a = Branch (Tree a) (Tree a) | Leaf a This is a recursive structure since a Tree can be made up of other Tree's. We can take a slice of the tree: data TreeNode a child = Branch child child | Leaf a data Fix f = F (f (Fix f)) type Tree a = Fix (TreeNode a) sumTree :: Tree Int -> Int sumTree = cata algebra where algebra (Branch a b) = a + b algebra (Leaf a) = a You might notice that we didn't do any recursion in sumTree because cata captures how to traverse the tree. Catamorphisms are the simplest recursion schemes, there are variants that keep track to our position in relation to the rest of the tree or memoize computations and so on.
    • bcherny 9y ago
      I see. You might pass a combinator into a catamorphism, but the morphism itself isn't a combinator?