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Refactor getContextDiffNumbered with separate Nothing equation #27

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Merged
ddssff merged 1 commit into from
Jun 4, 2026
+11 −13
Merged

Refactor getContextDiffNumbered with separate Nothing equation #27

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24 changes: 11 additions & 13 deletions src/Data/Algorithm/DiffContext.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -99,7 +99,8 @@ getContextDiffNumbered ::
-> [Numbered a]
-> [Numbered a]
-> ContextDiff (Numbered a)
getContextDiffNumbered contextSize a0 b0 =
getContextDiffNumbered Nothing a0 b0 = [getGroupedDiff a0 b0]
getContextDiffNumbered (Just contextSize) a0 b0 =
-- The 'Diff' list is grouped into 'Hunks' that begin and end
-- with matching ('Both') text, having non-matching ('First' and 'Second')
-- text in the middle. Note that a non-trivial partition can only happen after
Expand All @@ -125,8 +126,8 @@ getContextDiffNumbered contextSize a0 b0 =
doPrefix [Both _ _] = []
-- Do the prefix and then make the suffix.
doPrefix (Both xs ys : more) =
Both (maybe xs (\n -> drop (max 0 (length xs - n)) xs) contextSize)
(maybe ys (\n -> drop (max 0 (length ys - n)) ys) contextSize) : doSuffix more
Both (drop (length xs - contextSize) xs)
(drop (length ys - contextSize) ys) : doSuffix more
-- Prefix finished, do the diff then the following suffix.
doPrefix (d : ds) = doSuffix (d : ds)
-- | Handle the common text following a diff.
Expand All @@ -136,21 +137,18 @@ getContextDiffNumbered contextSize a0 b0 =
doSuffix :: Hunk a -> Hunk a
doSuffix [] = []
-- A trailing suffix.
doSuffix [Both xs ys] = [Both (maybe xs (\n -> take n xs) contextSize) (maybe ys (\n -> take n ys) contextSize)]
-- Either whole context or common text is too short to split.
doSuffix (Both xs ys : more)
| maybe True (\n -> length xs <= n * 2) contextSize =
Both xs ys : doPrefix more
doSuffix [Both xs ys] = [Both (take contextSize xs) (take contextSize ys)]
-- If the common text is too short compared with the context,
-- we preserve it and continue. As the following element cannot be a 'Both'
-- as well, this effectively places the common text in the inner part of the diff.
-- Otherwise, we split it into a suffix and prefix
-- (resulting in some elements excluded from the diff in the middle).
doSuffix (Both xs ys : more) =
-- NOTE: the guard above ensures that the following 'maybe's
-- default values are unreachable and result in non-empty lists.
Both (maybe xs (\n -> take n xs) contextSize) (maybe ys (\n -> take n ys) contextSize)
: doPrefix (Both (maybe mempty (\n -> drop n xs) contextSize) (maybe mempty (\n -> drop n ys) contextSize) : more)
doSuffix (Both xs ys : more)
| length xs <= contextSize * 2 =
Both xs ys : doPrefix more
| otherwise =
Both (take contextSize xs) (take contextSize ys) :
doPrefix (Both (drop contextSize xs) (drop contextSize ys) : more)
-- 'First' and 'Second' elements are no suffix, preserve them and continue looking.
doSuffix (d : ds) = d : doSuffix ds

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