[haskell-pipes] Re: Problem with Pipes.Text and processing two files

[Лев Никитин]

I'm trying to generate pairs of words from two files. Here is a Main.hs:


{-# LANGUAGE OverloadedStrings, FlexibleContexts #-}

import qualified Data.Text as T

import System.IO

import Control.Monad.Managed

import Pipes
import qualified Pipes.Prelude as P hiding (fromHandle)
import qualified Pipes.Text.IO as P
import qualified Pipes.Text as PT
import qualified Pipes.Group as PG
import Lens.Family (view)

inFile ⦂ FilePath → Managed Handle
inFile filePath = managed (withFile filePath ReadMode)

badTest ⦂ MonadIO m => Handle → Handle → Producer T.Text m ()
badTest names1 names2 =
  for (PG.concats ∘ view PT.lines $ P.fromHandle names1) $ λn1 →
    for (PG.concats ∘ view PT.lines $ P.fromHandle names2) $ λn2 → yield $
n1 `T.append` " ||| " `T.append` n2

goodTest ⦂ MonadIO m => Producer T.Text m ()
goodTest =
  for (each ["A", "B", "C", "D"]) $ λn1 →
    for (each ["1", "2", "3", "4"]) $ λn2 → yield $ n1 `T.append` " ||| "
`T.append` n2

main ⦂ IO ()
main = runManaged $ do
  names1 ← inFile "names1.txt"
  names2 ← inFile "names2.txt"
  liftIO $ runEffect $ badTest names1 names2 >-> P.map ((`T.append` "\n"))
>-> P.stdout
  liftIO $ putStrLn "-------------------------"
  liftIO $ runEffect $ goodTest >-> P.map ((`T.append` "\n")) >-> P.stdout


where names1.txt containts:
A
B
C
D

names2.txt:
1
2
3

I've got result:

A ||| 1
A ||| 2
A ||| 3
-------------------------
A ||| 1
A ||| 2
A ||| 3
A ||| 4
B ||| 1
B ||| 2
B ||| 3
B ||| 4
C ||| 1
C ||| 2
C ||| 3
C ||| 4
D ||| 1
D ||| 2
D ||| 3
D ||| 4

It means that badTest produces only first line of names1.txt file. But
similar goodTest does work right. What I am missed?

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A
B
C
D

{-# LANGUAGE OverloadedStrings, FlexibleContexts #-}

import qualified Data.Text as T

import System.IO

--import Control.Monad (forever)
import Control.Monad.Managed

import Pipes
import qualified Pipes.Prelude as P hiding (fromHandle)
import qualified Pipes.Text.IO as P
import qualified Pipes.Text as PT
import qualified Pipes.Group as PG
import Lens.Family (view)

inFile :: FilePath -> Managed Handle
inFile filePath = managed (withFile filePath ReadMode)

badTest :: MonadIO m => Handle -> Handle -> Producer T.Text m ()
badTest names1 names2 = 
  for (PG.concats . view PT.lines $ P.fromHandle names1) $ \n1 -> 
    for (PG.concats . view PT.lines $ P.fromHandle names2) $ \n2 -> yield $ n1 `T.append` " ||| " `T.append` n2

goodTest :: MonadIO m => Producer T.Text m ()
goodTest = 
  for (each ["A", "B", "C", "D"]) $ \n1 ->
    for (each ["1", "2", "3", "4"]) $ \n2 -> yield $ n1 `T.append` " ||| " `T.append` n2



main :: IO ()
main = runManaged $ do
  names1 <- inFile "names1.txt"
  names2 <- inFile "names2.txt"
  liftIO $ runEffect $ badTest names1 names2 >-> P.map ((`T.append` "\n")) >-> P.stdout
  liftIO $ putStrLn "-------------------------"
  liftIO $ runEffect $ goodTest >-> P.map ((`T.append` "\n")) >-> P.stdout

1
2
3

Preprocessing executable 'test-pipes' for test-pipes-0.1.0.0...
A ||| 1
A ||| 2
A ||| 3
-------------------------
A ||| 1
A ||| 2
A ||| 3
A ||| 4
B ||| 1
B ||| 2
B ||| 3
B ||| 4
C ||| 1
C ||| 2
C ||| 3
C ||| 4
D ||| 1
D ||| 2
D ||| 3
D ||| 4

import Distribution.Simple
main = defaultMain

test-pipes.cabal
Description: Binary data