I am just wondering whether we would want to add the
following to `MarshalError':
-- wrap the result into a `Maybe' type (EXPORTED)
--
-- * the predicate determines when the result is considered to be non-existing,
-- ie, it is represented by `Nothing'
--
-- * the second argument allows to map a result wrapped into `Just' to some
-- other domain
--
nothingIf :: (a -> Bool) -> (a -> b) -> a -> Maybe b
nothingIf p f x = if p x then Nothing else Just $ f x
-- instance for special casing null pointers (EXPORTED)
--
nothingIfNull :: (Ptr a -> b) -> Ptr a -> Maybe b
nothingIfNull = nothingIf (== nullPtr)
These are the `Maybe' counterparts of the exception routines
in MarshalError. This style of using `Maybe' for handling
special return values isn't covered by the `Maybe'-related
routines in `MarshalUtils'.
Cheers,
Manuel
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