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optimize compareSuffix a bit

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This commit is contained in:
Mitchell Rosen 2021-10-13 23:11:26 -04:00
parent ed0a850a56
commit fd99ecb1e1
1 changed files with 6 additions and 6 deletions
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12
unison-core/src/Unison/Name.hs
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@ -122,13 +122,13 @@ data Position
--
-- /O(n)/, where /n/ is the number of name segments.
compareSuffix :: Name -> Name -> Ordering
compareSuffix (Name _ ss0) (Name _ ss1) =
go (toList ss0) (toList ss1)
compareSuffix (Name _ ss0) =
foldr f (const EQ) ss0 . List.NonEmpty.toList . reverseSegments
where
go :: Ord a => [a] -> [a] -> Ordering
go [] _ = EQ -- only compare up to entire suffix (first arg)
go _ [] = LT
go (x : xs) (y : ys) = compare y x <> go xs ys
f :: NameSegment -> ([NameSegment] -> Ordering) -> ([NameSegment] -> Ordering)
f x acc = \case
[] -> LT
y : ys -> compare y x <> acc ys
-- | Cons a name segment onto the head of a relative name. Monotonic with respect to ordering: it is safe to use
-- @cons s@ as the first argument to @Map.mapKeysMonotonic@.