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