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module ImmutGrowVector where
import Foreign.Storable
import Data.Vector.Storable qualified as VS
-- | Acts like an immutable storable vector, except that it's split in a long
-- prefix and a short suffix so that modifications at the end are cheap. If the
-- suffix gets longer (by appending elements), the suffix elements are promoted
-- to prefix elements once in a while, resulting in a big copy at those times.
data ImmutGrowVector a = ImmutGrowVector (VS.Vector a) (VS.Vector a)
deriving (Show)
empty :: Storable a => ImmutGrowVector a
empty = ImmutGrowVector VS.empty VS.empty
fromListN :: Storable a => Int -> [a] -> ImmutGrowVector a
fromListN n l
| n > 2 =
let (l1, l2) = splitAt (n - 2) l
in ImmutGrowVector (VS.fromListN (n - 2) l1) (VS.fromListN 2 l2)
| otherwise =
ImmutGrowVector VS.empty (VS.fromListN n l)
(!) :: Storable a => ImmutGrowVector a -> Int -> a
ImmutGrowVector prefix suffix ! i
| i < VS.length prefix = prefix VS.! i
| otherwise = suffix VS.! (i - VS.length prefix)
length :: Storable a => ImmutGrowVector a -> Int
length (ImmutGrowVector prefix suffix) = VS.length prefix + VS.length suffix
set :: Storable a => ImmutGrowVector a -> Int -> a -> ImmutGrowVector a
set (ImmutGrowVector prefix suffix) idx value
| idx < VS.length prefix = error "ImmutGrowVector: mutation in slow part"
| otherwise = ImmutGrowVector prefix (suffix VS.// [(idx - VS.length prefix, value)])
append :: Storable a => ImmutGrowVector a -> a -> ImmutGrowVector a
append (ImmutGrowVector prefix suffix) value
| VS.length suffix < 8 = ImmutGrowVector prefix (suffix `VS.snoc` value)
| otherwise =
let n = VS.length suffix
in ImmutGrowVector (prefix <> VS.take (n - 1) suffix) (VS.drop (n - 1) suffix `VS.snoc` value)
|
