module FridaySession5 where

import Data.Maybe (fromJust,fromMaybe)

import Prelude hiding (seq)

mymap :: [(Int,[Int])]
mymap = [(1, [3,4,2,5]), (2,[6,5]), (3,[2,4,5,1,6]) ]

wrong :: Int
wrong = length $ lookup 2 mymap

correct :: Int
correct = length list where (Just list) = lookup 2 mymap

correct2 :: Int
correct2 = length (fromMaybe (error "Not found.") $ lookup 2 mymap)

correct3 :: Int
correct3 = length (fromJust $ lookup 2 mymap)

data UnOrdPair a = Pair (a,a)

instance (Show a, Ord a) => Show (UnOrdPair a) where
  show (Pair (x,y)) | x <= y    = "Pair (" ++ show x ++ "," ++ show y ++ ")"
                    | otherwise = "Pair (" ++ show y ++ "," ++ show x ++ ")"

instance Ord a => Eq (UnOrdPair a) where
  (==) (Pair (x1,y1)) (Pair (x2,y2)) = (x1==x2 && y1 == y2) || (x1==y2 && y1 == x2)