Yes, chop can be easily written in terms of unfoldr.  But the chop function fits better with other existing list functions, like I tried to illustrate with my examples.

  -- Lennart

On Tue, Dec 14, 2010 at 10:40 AM, Stefan Holdermans <stefan@vectorfabrics.com> wrote:
Henning,

>> I would like to propose the following function for inclusion in Data.List
>> chop :: (a -> (b, [a]) -> [a] -> [b]
>> chop _ [] = []
>> chop f as = b : chop f as'
>>   where (b, as') = f as


> Is the difference between 'unfoldr' and 'chop' just the Maybe result type of f?


Yes.

 chop f = unfoldr g
   where
     g [] = Nothing
     g as = Just (f as)

Cheers,

 Stefan