haskell - 如何使用管道将双选项卡替换为单选项卡？

Question

我需要用单个选项卡替换字节字符串中的所有连续选项卡，如下所示:

"___\t___\t\t___\t\t\t___"

变成了

"___\t___\t___\t___"

我不知道该怎么做。

经过半个小时的弄清楚，我成功地替换了第一次出现的双制表符，如下所示(即使这实际上是错误的 - 它向空字符串添加了一个制表符):

import qualified Pipes.ByteString as PB
import qualified Data.ByteString as B

removeConsecutiveTabs =
  PB.break (== tab) . mapped %~ \p -> do
    yield (B.singleton tab)
    PB.dropWhile (== tab) p

但是，我仍然不知道如何替换所有出现的连续选项卡。

Answer 1

试试这个:

{-# LANGUAGE OverloadedStrings #-}

import Pipes
import qualified Pipes.Prelude as P
import qualified Pipes.ByteString as PB
import           Data.ByteString (ByteString)
import Control.Lens hiding (each)

cleanTabs p = do
  p1 <- view (PB.span (/= 9)) p
  x <- lift $ next p1
  case x of
    Left r -> return r
    Right (a, p2) -> do
      yield "\t"
      let p3 = PB.dropWhile (== 9) (yield a >> p2)
      cleanTabs p3

source :: Monad m => Producer ByteString m ()
source = each [ "this", "is\t an", "\t\texample\t", "\t.", "\t\tmiddle\t", "\there"]

example = do
  putStrLn $ "input: " ++ (show $ P.toList source)
  putStrLn $ "output:" ++ (show $ P.toList (cleanTabs source))