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1−-----------------------------------------------------------------------------
3−-- Module : Data.Algorithm.Diff
4−-- Copyright : (c) Sterling Clover 2008
5−-- License : BSD 3 Clause
6−-- Maintainer : s.clover@gmail.com
7−-- Stability : experimental
8−-- Portability : portable
10−-- This is an implementation of the O(ND) diff algorithm as described in
11−-- \"An O(ND) Difference Algorithm and Its Variations (1986)\"
12−-- <http://citeseer.ist.psu.edu/myers86ond.html>. It is O(mn) in space.
13−-- The algorithm is the same one used by standared Unix diff.
14−-- The assumption is that users of this library will want to diff over
15−-- interesting things or peform interesting tasks with the results
16−-- (given that, otherwise, they would simply use the standard Unix diff
17−-- utility). Thus no attempt is made to present a fancier API to aid
18−-- in doing standard and uninteresting things with the results.
19−-----------------------------------------------------------------------------
21−module Diff (DI(..), getDiff, getGroupedDiff) where
25−-- | Difference Indicator. A value is either from the First list, the Second
27−data DI = F | S | B deriving (Show, Eq)
29−data DL = DL {poi::Int, poj::Int, path::[DI]} deriving (Show, Eq)
31−instance Ord DL where x <= y = poi x <= poi y
33−canDiag :: (Eq a) => [a] -> [a] -> Int -> Int -> (Int, Int) -> Bool
34−canDiag as bs lena lenb = \(i,j) ->
35− if i < lena && j < lenb then arAs ! i == arBs ! j else False
36− where arAs = listArray (0,lena - 1) as
37− arBs = listArray (0,lenb - 1) bs
39−chunk :: Int -> [a] -> [[a]]
40−chunk x = unfoldr (\a -> case splitAt x a of ([],[]) -> Nothing; a' -> Just a')
42−dstep :: ((Int,Int)->Bool) -> [DL] -> [DL]
43−dstep cd dls = map maximum $ [hd]:(chunk 2 rst)
44− where (hd:rst) = concatMap extend dls
45− extend dl = let pdl = path dl
46− in [addsnake cd $ dl {poi=poi dl + 1, path=(F : pdl)},
47− addsnake cd $ dl {poj=poj dl + 1, path=(S : pdl)}]
49−addsnake :: ((Int,Int)->Bool) -> DL -> DL
51− | cd (pi, pj) = addsnake cd $
52− dl {poi = pi + 1, poj = pj + 1, path=(B : path dl)}
54− where pi = poi dl; pj = poj dl
56−lcs :: (Eq a) => [a] -> [a] -> [DI]
57−lcs as bs = path . head . dropWhile (\dl -> poi dl /= lena || poj dl /= lenb) .
58− concat . iterate (dstep cd) . (:[]) . addsnake cd $
59− DL {poi=0,poj=0,path=[]}
60− where cd = canDiag as bs lena lenb
61− lena = length as; lenb = length bs
63−-- | Takes two lists and returns a list indicating the differences
65−getDiff :: (Eq t) => [t] -> [t] -> [(DI, t)]
66−getDiff a b = markup a b . reverse $ lcs a b
67− where markup (x:xs) ys (F:ds) = (F, x) : markup xs ys ds
68− markup xs (y:ys) (S:ds) = (S, y) : markup xs ys ds
69− markup (x:xs) (_:ys) (B:ds) = (B, x) : markup xs ys ds
72−-- | Takes two lists and returns a list indicating the differences
73−-- between them, grouped into chunks.
74−getGroupedDiff :: (Eq t) => [t] -> [t] -> [(DI, [t])]
75−getGroupedDiff a b = map go . groupBy (\x y -> fst x == fst y) $ getDiff a b
76− where go ((d,x) : xs) = (d, x : map snd xs)