Alex: strict and lazy bytestrings

Lazy.x

{
module Lazy where

import Data.Foldable
import qualified Data.ByteString.Lazy as B
}

%wrapper "basic-bytestring"

$alpha = [a-zA-Z]

words :-
  $white+       ;
  $alpha+       { \word -> B.snoc word 10 }

{
scanner :: B.ByteString -> Maybe [B.ByteString]
scanner str = go (AlexInput '\n' str 0)
  where
  go :: AlexInput -> Maybe [B.ByteString]
  go input@(AlexInput _ str _) =
    case alexScan input 0 of
      AlexEOF -> return []
      AlexError _ -> Nothing
      AlexSkip input _ -> go input
      AlexToken input len act -> do
        rest <- go input
        return $ act (B.take (fromIntegral len) str) : rest

main :: IO ()
main = do
  str <- B.takeWhile (/= 10) <$> B.getContents
  case scanner str of
    Just words -> traverse_ B.putStr words
    Nothing -> return ()
}

Strict.x

{
module Strict where

import Data.Foldable
import qualified Data.ByteString as B
}

%wrapper "strict-bytestring"

$alpha = [a-zA-Z]

words :-
  $white+       ;
  $alpha+       { \word -> B.snoc word 10 }

{
scanner :: B.ByteString -> Maybe [B.ByteString]
scanner str = go (AlexInput '\n' str 0)
  where
  go :: AlexInput -> Maybe [B.ByteString]
  go input@(AlexInput _ str _) =
    case alexScan input 0 of
      AlexEOF -> return []
      AlexError _ -> Nothing
      AlexSkip input _ -> go input
      AlexToken input len act -> do
        rest <- go input
        return $ act (B.take len str) : rest

main :: IO ()
main = do
  str <- B.getLine
  case scanner str of
    Just words -> traverse_ B.putStr words
    Nothing -> return ()
}