[Haskell-beginners] Why does this Ord-class instance crash?
rj248842 at hotmail.com
Fri May 21 08:13:41 EDT 2010
I'm trying to declare Triangle as an instance of the Ord class without using "deriving (Ord)", so I can better understand the manual instantiation.
As I understand it, all I need merely to define "<". Yet, when I do so using the code snippet below, this code hangs when I type "Scalene > Failure" in GHCi. Why is that, and what's the fix? Thanks.
data Triangle = Failure | Equilateral | Isosceles | Scalene deriving (Eq, Show)
instance Ord Triangle where Failure < Failure = False Failure < _ = True
Equilateral < Failure = False Equilateral < Equilateral = False Equilateral < _ = True
Isosceles < Scalene = True Isosceles < _ = False
Scalene < _ = False
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