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mxswd/gist:6666577

Created September 23, 2013 04:58
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gistfile1.hs
{-#LANGUAGE GADTs, EmptyDataDecls, DataKinds, KindSignatures #-}
-- kind
data ListCont = Empty | NonEmpty
data SafeList a (b :: ListCont) where
Nil :: SafeList a Empty
Cons:: a -> SafeList a b -> SafeList a NonEmpty
safeHead :: SafeList a NonEmpty -> a
safeHead (Cons x _) = x
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