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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