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25 lines
712 B
Haskell
25 lines
712 B
Haskell
module Patch where
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-- | An operation to replace, insert, or delete an item.
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data Patch a =
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Replace a a
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| Insert a
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| Delete a
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deriving (Functor, Show, Eq)
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-- | Return the item from the after side of the patch.
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after :: Patch a -> Maybe a
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after (Replace _ a) = Just a
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after (Insert a) = Just a
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after _ = Nothing
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-- | Return the item from the before side of the patch.
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before :: Patch a -> Maybe a
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before (Replace a _) = Just a
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before (Delete a) = Just a
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before _ = Nothing
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-- | Calculate the cost of the patch given a function to compute the cost of a item.
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patchSum :: (a -> Integer) -> Patch a -> Integer
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patchSum termCost patch = (maybe 0 termCost $ before patch) + (maybe 0 termCost $ after patch)
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