The dangers of incoherence

A.hs

module A where

newtype MyInt = MyInt {unMyInt :: Int}
  deriving (Show)

B.hs

module B where

import qualified Data.Map as Map
import Debug.Trace

import A

instance Eq MyInt where
  MyInt x == MyInt y = y == x

instance Ord MyInt where
  compare (MyInt x) (MyInt y) = compare y x

buildMap :: Map.Map MyInt MyInt
buildMap = Map.fromList $ zip (map MyInt [1..10]) (map MyInt [10,9..1])

C.hs

module C where

import qualified Data.Map as Map

import A

instance Eq MyInt where
  MyInt x == MyInt y = x == y

instance Ord MyInt where
  compare (MyInt x) (MyInt y) = compare x y

modifyMap :: Map.Map MyInt MyInt -> Map.Map MyInt MyInt
modifyMap = Map.insert (MyInt 0) (MyInt 0)

D.hs

module D where

import qualified Data.Map as Map

import A
import qualified B
import qualified C

main :: IO ()
main =
  print $ map unMyInt $ map fst $ Map.toAscList $ C.modifyMap $ B.buildMap