21 Aug
2003
21 Aug
'03
4:54 p.m.
tor 2003-08-21 klockan 22.26 skrev Jon Cast:
Yes. Many complicated proposals have been made, but there's a straightforward, general mechanism:
addMaybe :: Num alpha => Maybe alpha -> Maybe alpha -> Maybe alpha addMaybe a b = a >>= \x -> b >>= \y -> return (x + y)
or
addMaybe a b = do x <- a y <- b return (x + y)
or addMaybe = Monad.liftM2 (+) I personally use those monadic lifting functions a lot. Monad.sequence combined with list comprehension is another favorite. Regards, Martin