Add Tail module

src/Streamly/Coreutils/Tail.hs

@@ -0,0 +1,72 @@
+-- |
+-- Module      : Streamly.Coreutils.Tail
+-- Copyright   : (c) 2022 Composewell Technologies
+-- License     : Apache-2.0
+-- Maintainer  : [email protected]
+-- Stability   : experimental
+-- Portability : GHC
+--
+-- Output the last part of files.
+
+module Streamly.Coreutils.Tail
+
+    ( tail
+
+    -- * Options
+    , Tail
+    , follow
+    , tailN
+    )
+where
+
+import Control.Monad.IO.Class (MonadIO(liftIO))
+import Data.Function ((&))
+import Streamly.Prelude (SerialT)
+import System.IO (IOMode(..), openFile)
+
+import qualified Streamly.FileSystem.Handle as File
+import qualified Streamly.Internal.Data.Array as Array
+import qualified Streamly.Internal.Data.Stream.IsStream as Stream
+import qualified Streamly.Internal.Data.Fold as FL
+import qualified Streamly.Internal.Unicode.Stream as Unicode
+
+import Prelude hiding (tail)
+import Streamly.Coreutils.Common (Switch(..))
+
+newtype Tail = Tail{tailFollow :: Switch}
+
+defaultConfig :: Tail
+defaultConfig = Tail Off
+
+follow :: Switch -> Tail -> Tail
+follow opt cfg = cfg {tailFollow = opt}
+
+tailForEver :: Int -> FilePath -> SerialT IO [Char]
+tailForEver n fp = do
+    fh <- liftIO $ openFile fp ReadMode
+    Stream.concatMap Stream.fromList
+        $ Stream.repeatM
+        $ Stream.toList
+        $ Stream.unfold File.read fh
+        & Unicode.decodeUtf8
+        & Unicode.lines FL.toList
+        & Stream.fold (Array.writeLastN n)
+        & Stream.map Array.toStream
+        & Stream.concat
+
+tailN :: (Tail -> Tail) ->  Int -> FilePath -> SerialT IO [Char]
+tailN f n fp = do
+    fh <- liftIO $ openFile fp ReadMode
+    let opt = f defaultConfig
+    case tailFollow opt of
+        On -> tailForEver n fp
+        Off ->
+            Stream.unfold File.read fh
+                & Unicode.decodeUtf8
+                & Unicode.lines FL.toList
+                & Stream.fold (Array.writeLastN n)
+                & Stream.map Array.toStream
+                & Stream.concat
+
+tail :: (Tail -> Tail) -> FilePath -> SerialT IO [Char]
+tail f = tailN f 10

streamly-coreutils.cabal

@@ -92,13 +92,15 @@ library
     , unix >= 2.7.0 && < 2.8
     , directory >= 1.2.2 && < 1.4
     , data-default-class >= 0.1 && < 0.2
+    , monad-control    >= 1.0.3 && < 1.0.4
   hs-source-dirs:      src
   exposed-modules:
       Streamly.Coreutils
     , Streamly.Coreutils.Common
     , Streamly.Coreutils.Cp
     , Streamly.Coreutils.FileTest
     , Streamly.Coreutils.ShellWords
+    , Streamly.Coreutils.Tail
     , Streamly.Coreutils.Uniq
     , Streamly.Coreutils.Which