fiadliel

import com.ning.http.client._
import com.typesafe.scalalogging.StrictLogging
import scodec.bits.ByteVector

import scala.concurrent.duration._
import scalaz._
import scalaz.Scalaz._
import scalaz.concurrent.Task
import scalaz.stream._

joshcough

module Foo where

import Debug.Trace

traceByteString :: String -> ByteString -> ByteString
traceByteString msg b | traceShow b False = undefined
traceByteString msg b = b

gelisam

In response to this reddit post about failing to understand the Pipes library after a couple of hours. I wanted to show how an experienced haskeller does it, but I'm afraid it also took me quite a few hours, which is why the following list of steps goes on and on.

After all those hours, my opinion is that Pipes is not at all an easy library. I don't know if Conduit is any easier, but otherwise I side with your friend in advising to use something else (perhaps ordinary lazy IO?) instead of Pipes.

Anyway, here is the full brain dump of my steps as I tried to get your three snippets to fit together.

• Since you say that you have a hard time combining the snippets, I assume that they must have complicated types. So my first goal is to figure out the type of your first snippet.
• hoogle for parseUrl, withManager, etc. No results.
• Google for haskell runEffect, find that it's a method from Pipes.Core,