Thanks for the great feedback. The bijective example was especially interesting. While reading "Fun with Type Functions" I notices GNum as an interesting alternative to the Num type class but I couldn't find any such package on hackagedb. Do anyone know if there is anything like GNum on hackagedb? On an unrelated note: I hoogled "to" (i.e. http://haskell.org/hoogle/?hoogle=to) and just got a blank page. Nothing. Nil (not even <html>...</html>). Is this a bug or a "feature"? :) The reason I hoogled it was because I'm searching for something like explicit casting found in many other languages, something similar to
class To f t where to :: f -> t
instance To a a where to x = x
instance (Real a, Fractional b) => To a b where to = realToFrac
instance (Read a) => To String (Maybe a) where to = maybeRead -- not from cgi :)
so I can write something like
("23.2" `to`) :: Maybe Double
or
((42 :: Integer) `to`) :: Float
Anyone made a module/package that solves this problem already? I cannot be the first that needs generic type safe conversion... . -- Oscar