Comments on: More beautiful fold zipping http://conal.net/blog/posts/more-beautiful-fold-zipping Inspirations & experiments, mainly about denotative/functional programming in Haskell Sat, 26 Sep 2020 21:06:12 +0000 hourly 1 http://wordpress.org/?v=4.1.17 By: 什么# 39；如此糟糕，懒惰的I / O？ – CodingBlog http://conal.net/blog/posts/more-beautiful-fold-zipping#comment-50860 Wed, 31 May 2017 16:07:06 +0000 http://conal.net/blog/?p=59#comment-50860 […] inconvenient to have to do this for every stream processor. There are some generalizations (Conal Elliott – Beautiful Fold Zipping), but they don’t seem to have caught on. However, iteratees can get you a similar level of […]

]]> By: Edward Kmett http://conal.net/blog/posts/more-beautiful-fold-zipping#comment-198 Tue, 31 May 2011 22:54:44 +0000 http://conal.net/blog/?p=59#comment-198 FYI- In the newly broken out category-extras, the Apply class in semigroupoids provides the ‘Applicative-consistent’ semantics you noticed that you want for Zip here, while the Zip class in ‘keys’ provides the zip-like semantics.

]]> By: conal http://conal.net/blog/posts/more-beautiful-fold-zipping#comment-197 Mon, 23 Feb 2009 18:38:32 +0000 http://conal.net/blog/?p=59#comment-197 It recently hit me that Zip and zip aren’t such a great choice of names after all. I’d like the this notion to coincide with the Monoidal operation in section 7 of Applicative Programming with Effects, which must be consistent with Applicative instance. So the operation on lists would be cross product, not zip. On ZipList and Stream, zip is fine.

]]> By: conal http://conal.net/blog/posts/more-beautiful-fold-zipping#comment-196 Mon, 23 Feb 2009 18:37:44 +0000 http://conal.net/blog/?p=59#comment-196 Thanks for the pointer, Dan. I hadn’t explored that corner of category-extras. Will look further.

Meanwhile, here’s a tweaked definition of prod:

prod u v = (u . fmap fst) `zip` (u . fmap snd)

Or replace `zip` with &&&.

]]> By: Dan Piponi http://conal.net/blog/posts/more-beautiful-fold-zipping#comment-195 Mon, 23 Feb 2009 18:17:56 +0000 http://conal.net/blog/?p=59#comment-195 This zip for folds is a product in the category of certain F-algebras. More generally we can write:

import Control.Morphism.Cata

prod :: Functor f => Algebra f a -> Algebra f b -> Algebra f (a,b)
prod u v x = (u $ fmap fst x,v $ fmap snd x)

which generalises this to all catamorphisms.

]]> By: Conal Elliott » Blog Archive » Proofs for left fold zipping http://conal.net/blog/posts/more-beautiful-fold-zipping#comment-194 Sun, 15 Feb 2009 02:22:18 +0000 http://conal.net/blog/?p=59#comment-194 […] « More beautiful fold zipping Enhancing a Zip […]

]]> By: Conal Elliott » Blog Archive » Enhancing a Zip http://conal.net/blog/posts/more-beautiful-fold-zipping#comment-193 Sun, 16 Nov 2008 01:10:36 +0000 http://conal.net/blog/?p=59#comment-193 […] a pattern that’s been steering me lately toward natural (inevitable) design of libraries. * Part Two simplified that representation to help get to the essence of zipping, and in doing so lost the […]

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