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Document declarations in Patch.hs

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Matt Diephouse 2016-01-14 11:18:57 -05:00
parent 640449e2f3
commit 9c272a40d7
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src/Patch.hs
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@ -1,20 +1,24 @@
module Patch where
-- | An operation to replace, insert, or delete an item.
data Patch a =
Replace a a
| Insert a
| Delete a
deriving (Functor, Show, Eq)
-- | Return the item from the after side of the patch.
after :: Patch a -> Maybe a
after (Replace _ a) = Just a
after (Insert a) = Just a
after _ = Nothing
-- | Return the item from the before side of the patch.
before :: Patch a -> Maybe a
before (Replace a _) = Just a
before (Delete a) = Just a
before _ = Nothing
-- | Calculate the cost of the patch given a function to compute the cost of a item.
patchSum :: (a -> Integer) -> Patch a -> Integer
patchSum termCost patch = (maybe 0 termCost $ before patch) + (maybe 0 termCost $ after patch)