Doing exercises from "Haskell tutorial" ...

[Marcin 'Qrczak' Kowalczyk]

02 Oct 2001 15:16:27 +0300, Dmitry Astapov <adept@umc.com.ua> pisze:

> I need to define SetsAsLists as an instance of Set by supplying
> definitions for all Set methods, but definitions I wrote led me to
> adding additional constraints on "union" and "memeber" methods.

What constraints? The class already says that these operations require
Eq on the element type:

> class Set s where
>             empty :: s a
>             isEmpty :: s a -> Bool
>             singleton :: a -> s a
>             union :: Eq a => s a -> s a -> s a
                       ^^^^
>             member :: Eq a => a -> s a -> Bool
                        ^^^^
>             choice :: s a -> (a, s a)

-- 
 __("<  Marcin Kowalczyk * qrczak@knm.org.pl http://qrczak.ids.net.pl/
 \__/
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QRCZAK