More beautiful fold zipping
My previous post, Another lovely example of type class morphisms, placed some standard structure around Max Rabkin’s Beautiful folding, using type class morphisms to confirm that the Functor and Applicative instances agreed with their inevitable meanings.
In the process of working out the Applicative case, I realized the essence of fold zipping was getting a bit obscured.
This post simplifies Max’s Fold data type a bit and shows how to zip strict left folds in the simpler setting.
You can get the code described here.
Edits:
- 2008-11-15: I renamed the
PairandPair'classes toZipandZip'.