Justus Sagemüller leftaroundabout
leftaroundabout
/ Enum.hs
Created
April 1, 2012 23:22
— forked from depp/Enum.hs
Demonstration of how incorrect (Enum x, Enum y) => Enum (x, y) instance can be used for Enum a => Enum (a,a)
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| {-# LANGUAGE FlexibleInstances #-} | |
| -- See http://stackoverflow.com/questions/9967790/instance-in-haskell | |
| instance (Enum a) => Enum (a, a) where | |
| fromEnum (x,y) = | |
| k^2 + 2*j + if permuted then 1 else 0 | |
| where | |
| k = max (fromEnum x) (fromEnum y) | |
| j = min (fromEnum x) (fromEnum y) |