[Haskell-beginners] Making my own type belong to Data.Ord

[Patrik Iselind]

Den 2018-01-20 kl. 21:27, skrev Francesco Ariis:
> On Sat, Jan 20, 2018 at 09:20:33PM +0100, Patrik Iselind wrote:
>> It's the very last exercise on the page concerning constructing a Convex
>> Hull. I have no problem implementing a Graham Scan in non-functional
>> languages as i have far more experience with those. But the book hasn't yet
>> covered how i make my own data belong to for example the Data.Ord class. The
>> question then for me is how am i supposed to sort my coordinates?
>>
>> Type classes are not covered for another three chapters in the book. Given
>> this it seems to me that i should be able to solve this without using
>> Data.Ord, i just cannot see how. Any pointers would be highly appreciated.
> Hello Patrik,
>      as you suggested, implementing an instance of Data.Ord would be ok; if
> you don't want that
I wouldn't mind writing it, at all. It's probably the way i would do it 
if i knew more Haskell. My problem is just that the book i follow hasn't 
covered that topic yet, so even if i could google how to do it i guess i 
shouldn't until the book has covered the topic.

As i understand it this would be the 'preferred' way in the real world, 
is this correctly understood?
> , just write a
>
>      myTypeCompare :: SomeData -> SomeData -> Ordering
>
> function to use with `sortBy` from `Data.List`.
> Does that make sense?
That would make sense, i seem to remember something along those lines 
from previous topics covered in the book.

Thanks a lot Francesco, much appreciated!

// Patrik