Hi, I'm trying to follow the "Real World Haskell" book online and have reached exercise 12 in chapter three. See the bottom of http://book.realworldhaskell.org/read/defining-types-streamlining-functions.... for reference. 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. -- Patrik Iselind