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'combine' function pulled out and named and exported, with documentation #4

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'combine' function pulled out and named and exported, with documentation #4

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30 changes: 21 additions & 9 deletions src/Data/Algorithm/Diff3.hs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
{-| An implementation of a 3-way merge algorithm. -}
module Data.Algorithm.Diff3 (Hunk(..), diff3, merge) where
module Data.Algorithm.Diff3 (Hunk(..), diff3, combine, merge) where

import Data.Algorithm.Diff
import Data.Monoid (Monoid, mempty, mappend)
Expand Down Expand Up @@ -29,15 +29,27 @@ instance Functor Hunk where
-- a \'low level\' interface to the 3-way diff algorithm - you may be more
-- interested in 'merge'.
diff3 :: Eq a => [a] -> [a] -> [a] -> [Hunk a]
diff3 a o b = step (getDiff o a) (getDiff o b)
diff3 a o b = combine (getDiff o a) (getDiff o b)

--------------------------------------------------------------------------------
-- | Combine two list of 'Diff's representing two diverging changes from
-- the __same__ original document into a list of 'Hunk's representing
-- a three-way merge.
--
-- Behavior is undefined if the two inputs do not come from diffs from the
-- same original document.
--
-- @
-- 'diff3' a o b = 'combine' ('getDiff' o a) ('getDiff' o b)
-- @
combine :: [Diff a] -> [Diff a] -> [Hunk a]
combine [] [] = []
combine [] ob = toHunk [] ob
combine oa [] = toHunk oa []
combine oa ob = conflictHunk ++ matchHunk ++ combine ra' rb'
where
step [] [] = []
step [] ob = toHunk [] ob
step oa [] = toHunk oa []
step oa ob =
let (conflictHunk, ra, rb) = shortestConflict oa ob
(matchHunk, ra', rb') = shortestMatch ra rb
in conflictHunk ++ matchHunk ++ step ra' rb'
(conflictHunk, ra, rb) = shortestConflict oa ob
(matchHunk, ra', rb') = shortestMatch ra rb


--------------------------------------------------------------------------------
Expand Down