This is also quite similar to what we have in SmallCheck:
https://github.com/feuerbach/smallcheck/blob/master/Test/SmallCheck/Series.h...
Not sure how to exploit this, though.
* Sjoerd Visscher
I am pleased to announce the 5th version of the unfoldable package. (This is the first announcement, you didn't miss anything.) http://hackage.haskell.org/package/unfoldable-0.4.0
Just as there's a Foldable class, there should also be an Unfoldable class. This package provides one:
class Unfoldable t where unfold :: Unfolder f => f a -> f (t a)
Writing instances of Unfoldable is similar to writing Traversable instances. For example, given a data type
data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)
a suitable instance would be
instance Unfoldable Tree where unfold fa = choose [ pure Empty , Leaf <$> fa , Node <$> unfold fa <*> fa <*> unfold fa ]
The choose function comes from the Unfolder class:
class Applicative f => Unfolder f where choose :: [f x] -> f x
(If f is an Alternative instance, choose is simply Data.Foldable.asum.)
Different unfolders provide different ways of generating values, for example: - Random values - Enumeration of all values (depth-first or breadth-first) - Convert from a list - An implementation of QuickCheck's arbitrary should also be possible (still working on that)
Some examples can be found in the examples directory in the github repo: https://github.com/sjoerdvisscher/unfoldable
Ideas and comments are welcome!
greetings, Sjoerd
-- Roman I. Cheplyaka :: http://ro-che.info/