Awesome, that helps a lot.
Thanks a bunch, Mateusz!
Regards,
Tyler Huffman
On Sun, Mar 2, 2014 at 10:44 PM, Mateusz Kowalczyk
On 03/03/14 05:33, Tyler Huffman wrote:
Hi all,
I'm having trouble finding resources explaining how Ord for two lists works.
I've created a public gist to explain what I mean.
https://gist.github.com/iduhetonas/9318958
Could anybody shed some light on what I'm seeing?
Regards, Tyler Huffman
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It does element-wise comparisons and in case one of the lists is empty, the other one is considered greater (unless they are both empty).
So: Prelude> max [1] [2]
Here 2 is bigger than 1 so we get the result straight away
Prelude> max [1,2] [1]
Here the first element is equal so we compare the rest of lists: [2] and []. As the second list is empty, we return the first list.
Prelude> max [2,1] [1]
No problem at all here, 2 is greater than 1 so we just return the first list on the first comparison.
Prelude> max [1,2] [1,2,4]
This is exactly the same case as ‘max [1, 2] [1]’: we first compare the 1s, find they are equal and compare the rest of the list. Same with 2s. Then the base case is ‘max [] [4]’ so the second list is treated as greater.
Prelude> max [1,2,4] [1,2]
Same as above but with arguments switched. I believe that the law here is ‘max x y ≡ max y x’.
Prelude> max [[1,2,3],[2,3,4]] [[1,2],[2,3],[2,4]]
This is just like all our other examples except one more level of nesting. We first end up comparing the first elements of the argument (so we call out ‘max [1, 2, 3] [1, 2]’, and then check each element of these lists. 1 and 2 are equal and we reach the ‘max [3] []’ case: the first list was greater so our whole call returns ‘[[1, 2, 3], [2, 3, 4]]’.
I hope that sheds some light.
-- Mateusz K. _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners