[Haskell-beginners] Defining an Instance of Ord

[Petr Vápenka]

What about using new type and sort the pair before comparing?
Dne 26.6.2015 15:56 "Matt Williams" <matt.williams45.mw at gmail.com>
napsal(a):

> Dear All,
>
> I am trying to produce a Map, where the (tricky) idea is that the key is a
> pair, (t1, t2), and the key is considered identical under ordering. Thus:
>
> (t1, t2) is the same as (t2, t1) but
> (t1, t3) is not the same as (t1,t2).
>
> This LOOKS like a equality definition. However, the Map key typeclass is
> defined as Ord, which requires me to define compare:
>
> instance Ord Edge where
>   (Edge s1 _) `compare` (Edge s2 _) = s1 `compare` s2
>
> I am a bit stuck on how to use compare to define this type of eqlaity - any pointers very gratefully received.
>
> BW,
>
> Matt
>
>
>
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