[Haskell-cafe] Is this haskelly enough?

Dan Weston westondan at imageworks.com
Tue Jul 17 19:18:51 EDT 2007

Nicest. I think your definition has reached nirvana.

I think a good haskell-cafe thread is like a Shakespeare play. People at 
every level of experience can get something from it. The early replies 
answer the question, with follow-on ones exploring the roads less 
traveled. I for one did not know how to construct the fully pointless 
version below, and if I hadn't asked, I doubt I ever would.

I also learned of the list monad this exact same way, so I think its a 
good and gentle way to introduce people to it.


Bjorn Bringert wrote:
> On Jul 18, 2007, at 1:00 , Dan Weston wrote:
>> Bjorn Bringert wrote:
>>> import Data.List
>>> maxsubarrays xs = maximumBy (compare `on` sum)
>>>   [zs | ys <- inits xs, zs <- tails ys]
>> I love this solution: simple, understandable, elegant.
>> As a nit, I might take out the ys and zs names, which obscure the fact 
>> that there is a hidden symmetry in the problem:
>> maxsubarrays xs = pickBest  (return xs >>= inits >>= tails)
>>  where pickBest = maximumBy (compare `on` sum)
>>   -- NOTE: Since pickBest is invariant under permutation of its arg,
>>   --       the order of inits and tails above may be reversed.
>> Dan Weston
> Nice. Here's a pointless version:
> maxsubarrays = maximumBy (compare `on` sum) . (>>= tails) . inits
> Though I avoided using the list monad in the first solution, since I 
> thought it would make the code less understandable for a beginner.
> /Björn

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