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Today's Topics:
1. Why does this Ord-class instance crash? (R J)
2. Re: Why does this Ord-class instance crash?
(Brandon S. Allbery KF8NH)
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Message: 1
Date: Fri, 21 May 2010 12:13:41 +0000
From: R J <[email protected]>
Subject: [Haskell-beginners] Why does this Ord-class instance crash?
To: <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
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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Message: 2
Date: Sat, 22 May 2010 17:22:21 -0400
From: "Brandon S. Allbery KF8NH" <[email protected]>
Subject: Re: [Haskell-beginners] Why does this Ord-class instance
crash?
To: R J <[email protected]>
Cc: [email protected]
Message-ID: <[email protected]>
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