On Fri, 2008-10-31 at 18:43 -0200, Mauricio wrote:
Hi,
After a lot of thinking, I can't get what I am doing wrong in this code:
------ data ( RandomGen g ) => RandomMonad g a = RandomMonad (g -> a)
instance Monad (RandomMonad g) where return = RandomMonad . const RandomMonad f1 >>= f2 = RandomMonad f3 where f3 a = f2f1 a (next a) RandomMonad f2f1 = f2 . f1 ------
I get this error message:
Could not deduce (RandomGen g) from the context (Monad (RandomMonad g)) arising from a use of `RandomMonad' at src/encherDB.hs:10:11-21 Possible fix: add (RandomGen g) to the context of the type signature for `return' In the first argument of `(.)', namely `RandomMonad' In the expression: RandomMonad . const In the definition of `return': return = RandomMonad . const
but I'm not smart enough to understand what it means.
Yikes. Just search the archives for `Set not a Monad'; you have the same issue. Hint: data RandomGen g => RandomMonad g a means nothing at all like what you think it means. jcc