Monads and Maybe

[Jon Cast]

> 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.

So do I.  But that style doesn't work as well with functions that are
already in the monad.  So, I mentioned the more general style.

Jon Cast