`pipes` is a group of libraries written in Haskell to provide safe, functional, and strict I/O.
Questions tagged [haskell-pipes]
139 questions
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Understanding error in haskell
I (New to Haskell) am trying to perform unpack operation on ByteString that I receive from webpage. Basically I want to search few words from webpage so I am trying to tokenize stream, then search word from words.
Prelude Network.HTTP.Conduit LB>…
Manvi
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Haskell Pipes and testing with HSpec
I have written a program for a project that uses Pipes, which I love! I'm struggling to unit test my code however.
I have a series of functions of type Pipe In Out IO () (for example) that I wish to test with HSpec. How can I go about this?
For…
Alex
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Decoding JSON stream where some values are needed before others
Let us say we have a JSON object like this (with base64 encoded bytestring):
TaggedImage = TaggedImage { id :: Text, image :: ByteString }
Now, we want to receive image from a source, and store it in a location using the information in id tag. So,…
Sal
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Error handling in pipes
Backstory
I have a number of data files, each of them containing a list of data records (one per line).
Similar to CSV but sufficiently different that I'd prefer to write my own parser rather than using a CSV library.
For the purpose of this…
Lemming
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Catching exceptions in monad transformers
I'm using haskell-pipes to recursively traverse a directory and print the files. How do I handle exceptions from the Producer, which is a monad transformer? bracket and handle do not work in this case.
import Control.Exception (handle,…
Jan Synáček
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Haskell Pipes: How do I sort the output of a producer?
I have the following piece of code:
import Control.Monad (unless)
import Pipes
import qualified Pipes.Prelude as P
import System.FilePath.Posix (())
import System.Posix.Directory (DirStream, openDirStream, readDirStream)
produceFiles ::…
Jan Synáček
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Pipe that maintains state
I'm trying to calculate rolling hash values (buzzhash) for a big file using pipes.
Currently I have this. But don't know how to write a pipe that maintains a state.
import qualified Data.ByteString.Lazy as L
import Data.Word
import…
Dulguun Otgon
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Haskell-pipes: how to use drawAll to test a producer with a MonadSafe constraint?
I have a producer which, given a path, traverses the filesystem yielding Haskell files' paths. It's built on top of pipes-files:
import Pipes
import Pipes.Files
import Pipes.Safe
import qualified Pipes.Prelude as P
import Data.Monoid ((<>))
import…
rubik
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Using Pipes.Safe with IO actions
I'm using Pipes.Files, which in turn relies upon Pipes.Safe. I have a pipeline like this:
import Pipes
import Pipes.Files
import Pipes.Safe
import qualified Pipes.Prelude as P
allFiles :: (MonadIO m, MonadSafe m) => FilePath -> Producer FilePath m…
rubik
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Forking the streaming flow in haskell-pipes
I'm having trouble directing flow though a pipeline with haskell-pipes. Basically, I analyze a bunch of files and then I have to either
print results to the terminal in a human-friendly way
encode results to JSON
The chosen path depends upon a…
rubik
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Pipes get Network.Socket.ByteString.recv: failed (Unknown error)
Maybe a silly way to do things, but here it goes. I wanted to split the HTTP request send/receive from processing the response.
import Pipes
import qualified Pipes.HTTP as HTTP
import Pipes.Core
import qualified Pipes.ByteString as PB
import…
Sassa NF
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Could GHC be enhanced to print type aliases in error messages?
I'm wondering if this would be a reasonable feature request (even better if it already exists and I don't know how to access it).
An example of why this is desirable is the pipes library. Pipes defines a type:
data Proxy a' a b' b m r
with a ton of…
Michael Fox
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replacing an element in a list of lists -- haskell
I have this code :
type Matrice = [[String]]
matr =[[" - "," 0 "," - "],[" - "," - "," - "],[" - "," - "," - "]]
changeValue :: Matrice ->Int->Int->Matrice
changeValue mat x y = [
if ((mat !! x) !! y) /= " - "
then mat
…
Sami Li
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Sleeping with pipes in Haste and Haskell
I'm working on a Haskell program that makes heavy use of the Pipes library. I'm porting part of the library to Haste. The one place where I've hit a stumbling block is in the odd way that javascript handles sleeping.
What I wanted to write was a…
rprospero
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pipes for each evaluates before sending downstream?
going through the pipes tutorial led to toying with some examples:
import Pipes
import qualified Pipes.Prelude as P
f1 :: Show a => Int -> [a] -> IO ()
f1 n xs = runEffect $ (for (each xs) (lift . putStrLn . show))
>-> P.take n
…
sreekar
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