Hi, Am Mittwoch, den 30.11.2011, 10:51 -0200 schrieb Felipe Almeida Lessa:
How about using the Down/Dual/Desc/Converse/Opposite/Reverse newtype discussed in another recent thread, and providing for Data.Map:
reverse :: Map k a -> Map (Reverse k) a reverse Tip = Tip reverse (Bin n k a l r) = Bin n (Reverse k) a (reverse r) (reverse l)
(Arguably we also need reverse' :: Map (Reverse k) a -> Map k a. Hmm...)
reverse' :: Map (Reverse k) a -> Map k a reverse' = unsafeCoerce . reverse
Sorry, couldn't resist =).
have used unsafeCoerce to change the type inside a container to a "type" alias in real code, but your post makes me wonder: Under what circumstances is that safe? Is that documented somehow? Can a tool or the compiler decide for us whether it is safe? Thanks, Joachim -- Joachim "nomeata" Breitner mail@joachim-breitner.de | nomeata@debian.org | GPG: 0x4743206C xmpp: nomeata@joachim-breitner.de | http://www.joachim-breitner.de/