Re: [Haskell-cafe] The Typeable class is changing

11 Jul 2011


      I hope that typeRepKey is no longer in the IO monad (for the simple reason to
teach me that the key can change between session). This forced me to use
unsafePerformIO to make a typeable boxed type of instances of Ord an
instance of Ord (to put it in a Map). Or did I miss something and I can do
better anyhow?

e.g.:
class (Ord s, Typeable s) => Selector s
data GenSelector = forall s . Selector s =>  GS s

instance Ord GenSelector where
    compare (GS a) (GS b) = if typeOf a == typeOf b then
                    compare (fromJust (cast a)) b
                    else compare (unsafePerformIO $ typeRepKey $ typeOf a)
                                 (unsafePerformIO $ typeRepKey $ typeOf b)

Jürgen Nicklisch
 

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Re: [Haskell-cafe] The Typeable class is changing

jutaro