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February 2001

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22 discussions

RE: MarshalError
by Simon Marlow 08 Feb '01

08 Feb '01

> Sun, 04 Feb 2001 17:15:16 +1100, Manuel M. T. Chakravarty > <chak(a)cse.unsw.edu.au> pisze: > > > I am just wondering whether we would want to add the > > following to `MarshalError': > > Maybe throwIf should be changed to failIf? The same function would > work for both IO and Maybe. I don't see that. Presumably you mean overloading failIf with the Monad class, but `fail' takes a String and in the IO monad we want to raise a real IOError, not just a UserError. Cheers, Simon

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MarshalError
by Manuel M. T. Chakravarty 04 Feb '01

04 Feb '01

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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