[Haskell-cafe] Problem with pipe/Is there a function that "lifts" functions to Producers?

[Cody Goodman]

My first problem is that I was assuming each chunk was the entire line.

On Fri, Jun 30, 2017 at 12:08 AM, Cody Goodman <
codygman.consulting at gmail.com> wrote:

> Hi all,
>
> I have a function from Text -> Text which I want to apply to each line
> using pipes-text and pipes-group.
>
>
> I'm pretty sure my pipe is not doing what I expect. I'm going back over
> the pipes tutorial now, but I think I could use some help figuring it out.
>
> I have the following (buildable github project:
> https://github.com/codygman/fixedWidthToDelimited) code:
>
> import Data.Monoid
> import Pipes
> import qualified Pipes.Text as Text
> import qualified Pipes.Text.IO as Text
> import System.IO
> import Lens.Family
> import qualified Pipes.Group as Group
> import qualified Data.Text as T
>
>
>
> appendAt :: Int -> T.Text -> T.Text -> (T.Text,T.Text)
> appendAt i appendBS bs = let (first, rest) = T.splitAt i bs in (first <>
> appendBS <> rest,rest)
>
> -- TODO figure out how to test a pipe (I'm sure pipes-text or any other
> libraries test their pipes)
> toDelimPipe :: Monad m => [Int] -> Pipe T.Text T.Text m r
> toDelimPipe offsets = do
>     chunk <- await
>     let text = (fixedWidthLine offsets) chunk
>     if T.null text
>       then (toDelimPipe offsets)
>       else do yield text
>               cat
>
> fixedWidthLine :: [Int] -> T.Text -> T.Text
> fixedWidthLine offsets bs = fst $ go offsets ("" :: T.Text,bs)
>   where go :: [Int] -> (T.Text,T.Text) -> (T.Text,T.Text)
>         go [] x = x
>         go (x:xs) (acc,rest) = let (newAcc,newRest) = T.splitAt x rest in
> go xs (acc <> (fst $ appendAt x "|" newAcc),newRest)
>
> {-
> got:
> runEffect $ over Text.lines (Group.maps (>-> toDelimPipe [2,2,2] ))
> (Text.fromLazy (LT.replicate 2 "x" <> LT.replicate 2 "y" <> LT.replicate 2
> "z")) >-> Text.stdout
> xx|||yyzz
>
> Expected:
>
> xx|yy|zz|
>
> When I use fixedWidthLine alone with the same offsets I get:
>
> λ> fixedWidthLine [2,2,2] (T.replicate 2 "x" <> T.replicate 2 "y" <>
> T.replicate 2 "z")
> "xx|yy|zz|"
>
> I think my pipe is wrong
>
> -}
>
>
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