Opps... Yes. You are right. Thanks.
As I understand if names2.txt is a "big" file this is a best way to process
it.
Another way is to load all data of the file into memory (to [], for
example).
Or there is another better way to generate all combinations of data?
пятница, 6 февраля 2015 г., 0:06:14 UTC+6 пользователь Лев Никитин написал:
>
>
> 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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