I'm having a problem using `liftM`. For `(+)` it works fine, the function
`madd a b = liftM2 (+) a b`gives me the expected result `Just 5 `madd` Just 7 = Just 12`
but now trying it with `(/)` it gives me strange results.

`mdiv a b = liftM2 (/) a b` now the operation `Just 12 `mdiv` Just 0` gives me `Just Infinity`
while I'm expecting `Nothing`.