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* Add lazy dropEnd and friends Fixes #306. Utilizes an eager strategy as described in the original issue. Chunks are eagerly evaluated but the overall structure and pointers are kept intact. * Fix `since` version number * Use `foldrChunks` instead of `length` based checks * Add review changes - Pass Int64 to accumulators - Clean up `breakEnd` - Implement lazy version of `dropWhileEnd` - Add dropWhileEnd lazy test * Fix `breakEnd` and `spanEnd` lazyness * Make `dropEnd` lazier * Formatting * Fix lazy `dropEnd` * Add `Deque` module `dropEnd` now uses `Deque` for handling the accumulated bytestrigs * Normalize function names * Return `Maybe (S.ByteString, Deque)` from pops Plus all other review suggestions * Add review changes * Rename `dropElements` to `dropEndBytes` * Add examples + style fixes * Update Data/ByteString/Lazy/Internal/Deque.hs Co-authored-by: Simon Jakobi <simon.jakobi@gmail.com> * Replace `elemLength` with `byteLength` * Upadate examples Co-authored-by: Simon Jakobi <simon.jakobi@gmail.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,66 @@ | ||
| {- | | ||
| A Deque used for accumulating `S.ByteString`s in the lazy | ||
| version of `dropEnd`. | ||
| -} | ||
| module Data.ByteString.Lazy.Internal.Deque ( | ||
| Deque (..), | ||
| empty, | ||
| null, | ||
| cons, | ||
| snoc, | ||
| popFront, | ||
| popRear, | ||
| ) where | ||
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| import qualified Data.ByteString as S | ||
| import Data.Int (Int64) | ||
| import Prelude hiding (head, length, null) | ||
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| -- A `S.ByteString` Deque used as an accumulator for lazy | ||
| -- Bytestring operations | ||
| data Deque = Deque | ||
| { front :: [S.ByteString] | ||
| , rear :: [S.ByteString] | ||
| , -- | Total length in bytes | ||
| byteLength :: !Int64 | ||
| } | ||
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| -- An empty Deque | ||
| empty :: Deque | ||
| empty = Deque [] [] 0 | ||
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| -- Is the `Deque` empty? | ||
| -- O(1) | ||
| null :: Deque -> Bool | ||
| null deque = byteLength deque == 0 | ||
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| -- Add a `S.ByteString` to the front of the `Deque` | ||
| -- O(1) | ||
| cons :: S.ByteString -> Deque -> Deque | ||
| cons x (Deque fs rs acc) = Deque (x : fs) rs (acc + len x) | ||
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| -- Add a `S.ByteString` to the rear of the `Deque` | ||
| -- O(1) | ||
| snoc :: S.ByteString -> Deque -> Deque | ||
| snoc x (Deque fs rs acc) = Deque fs (x : rs) (acc + len x) | ||
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| len :: S.ByteString -> Int64 | ||
| len x = fromIntegral $ S.length x | ||
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| -- Pop a `S.ByteString` from the front of the `Deque` | ||
| -- Returns the bytestring and the updated Deque, or Nothing if the Deque is empty | ||
| -- O(1) , occasionally O(n) | ||
| popFront :: Deque -> Maybe (S.ByteString, Deque) | ||
| popFront (Deque [] rs acc) = case reverse rs of | ||
| [] -> Nothing | ||
| x : xs -> Just (x, Deque xs [] (acc - len x)) | ||
| popFront (Deque (x : xs) rs acc) = Just (x, Deque xs rs (acc - len x)) | ||
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| -- Pop a `S.ByteString` from the rear of the `Deque` | ||
| -- Returns the bytestring and the updated Deque, or Nothing if the Deque is empty | ||
| -- O(1) , occasionally O(n) | ||
| popRear :: Deque -> Maybe (Deque, S.ByteString) | ||
| popRear (Deque fs [] acc) = case reverse fs of | ||
| [] -> Nothing | ||
| x : xs -> Just (Deque [] xs (acc - len x), x) | ||
| popRear (Deque fs (x : xs) acc) = Just (Deque fs xs (acc - len x), x) |
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