Remove unsafe implementation of vacuous/vacuousM #3
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Come to think of it, you might be able to do this without GADTs too, e.g. by using Leibniz equality. |
Unfortunately, you can use these to derive unsafeCoerce:
import Data.Void
data Iso a b = Iso { to :: a -> b, from :: b -> a }
instance Functor (Iso a) where
fmap = undefined
lie :: Iso Void a
lie = vacuous (Iso id id)
evil :: a -> b
evil = to lie . from lie
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I was right; here's a Haskell 98 version of the trick. I've updated the commit message accordingly. |
ekmett
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Dec 2, 2012
Remove unsafe implementation of vacuous/vacuousM
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Unfortunately, you can use GADTs to derive
unsafeCoercefrom this implementation; see http://lpaste.net/78660.Perhaps the faster version should be exported as
unsafeVacuous, possibly from another module (e.g.Data.Void.Unsafe)?