David Roundy wrote:
Try
module Secret (Secret, classify, declassify)
where
data Secret a = Secret String a
classify :: String -> a -> Secret a
classify pw x = Secret pw x
declassify :: Secret a -> String -> Maybe a
declassify (Secret pw x) pw' | pw' == pw = Just x
declassify (Secret _ _) _ = Nothing
instance Monad Secret where
return = classify ""
(Secret pw x) >>= f = case f x of
Secret _ y -> Secret pw y
That's just the sort of thing I was looking for. Thanks!
Arie Peterson wrote:
What should 'q >>= r' mean, when 'q' and 'r x' are secrets with different
passwords? In the code above, the result is a secret with the same
password as 'q'. This allows you to declassify any secret without knowing
its password:
Yeah, but I think that's easy to fix: make classify and declassify take
a set of strings rather than a single string, and then make >>= return a
secret containing the union of passwords on both sides.
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