+1 for the inclusion of chop.
The unfoldr relationship is a good thing, because it gives an insight into
when you can do 'chop fusion' by leaning on the unfoldr/destroy rules. ;)
If we actually used unfoldr/destroy fusion, I'd probably advocate for
defining chop in terms of unfoldr as a consequence, to facilitate rewriting,
but noting the relationship at least provides a nice way to handle it for
the stream fusion folks.
-Edward
On Tue, Dec 14, 2010 at 10:38 AM, Lennart Augustsson wrote: 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 _______________________________________________
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