Folks [statutory warning: functors, terminal objects, unsafeCoerce]
I had a peculiar notion this morning to wonder whether I could get away with shape :: Functor f => f a -> f () shape fa = unsafeCoerce fa Sure enough, ghci gives me *Top> shape "moo" [(),(),()] *Top> shape [undefined] [*** Exception: Prelude.undefined which shows that pattern matching does just enough work to check that an element of () isn't bottom. I'm just wondering if that's really what's happening, what other implementations do, and how the garbage collector would react: would all those a's hang around for as long as the shape? I'm also wondering whether it makes sense to have a "bottomless Top" type, with constructor _ and lazy pattern _ (with (undefined :: Top) equal to _). Then the constant-time shape operator makes the same sort of sense as the constant-time inflate :: Functor f => f Zero -> f a Any thoughts on either or both? Cheers Conor _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
