By: Andrew

Andrew — Tue, 04 Jan 2011 22:20:42 +0000

Thanks for the blog post (and the WGP paper is also nice). Looks like that’s exactly what I need. Are you still supporting the Annotations library?

By: Aycan iRiCAN

Aycan iRiCAN — Sat, 26 Jun 2010 00:12:24 +0000

Very nice blog. I was reading Sebastiaan Visser’s msc thesis which also uses FixF for annotating recursive types. Thank you.

Edward Kmett — Thu, 24 Jun 2010 19:07:56 +0000

AnnFix is the f-branching stream/cofree comonad (with the arguments flipped around).

I tend to like to express it with:

data f :> a = a :< f (f :> a)

it is available in Control.Comonad.Cofree in category-extras

or in Numeric.AD.Types from ‘ad’ as Stream.

You may find the following bits and pieces enlightening:

http://comonad.com/reader/2009/incremental-folds/ puts the (:>) type above to use, and calculates those annotations using f-algebras using smart constructors.

http://splonderzoek.blogspot.com/2010/03/final-push-ups-push-downs-and-passing.html is Leather, Loeh, and Jeuring’s take on the same thing. They, like you, and my code in category-extras, chose to separate the fixed point from Ann. They provide a similar incremental fold to the code in my blog, but with less type safety.