I suspect the problem is that in "badTest", the "names2" handle is
exhausted after the first execution of the inner loop, and subsequent reads
do not produce anything. Perhaps you could invoke hSeek at the beginning of
the inner loop.
On Thursday, February 5, 2015 at 7:06:14 PM UTC+1, Лев Никитин wrote:
>
>
> 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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