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Questions tagged [haskell-pipes]

`pipes` is a group of libraries written in Haskell to provide safe, functional, and strict I/O.

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Clarification on Streaming and Effects in context of Pipes Library

The pipes tutorial have mentioned this in their documentation: If you sacrifice Effects you get Haskell's pure and lazy lists, which you can transform using composable functions in constant space, but without interleaving effects. If you sacrifice…
Sibi
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In Haskell, how do I promptly close resources?

Old pipes tutorial has following example. How would this code look like with version 4.1.1? read' :: FilePath -> Frame Text IO C C () read' file = do liftU $ putStrLn "Opening file..." h <- liftU $ openFile file ReadMode -- The…
Rumca
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Catching exceptions in a pipe without terminating it

This feels like kind of a long shot, but I wrote a pipe to connect to a database, get a list of databases on the server, connect to each one, then perform a query on each one (a user count), then print those counts. Unfortunately this is about as…
David McHealy
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Typechecking problems with pipes-attoparsec

I've been trying out pipes-attoparsec but haven't been having much luck. It appears that there is a type mismatch between Void and X in (what seems to be) relatively straightforward code. From what I've read in the library (that this will be a type…
user1219
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How to "vertically stack" Control.Frames?

In the pipes package, the tutorial Control.Pipes.Tutorial [1] shows how to "vertically stack" pipe components using the monad >> operator. How would I go about doing that with Control.Frame? For example, using the definitions from the Control.Frame…
ErikR
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Await with timeout using purescript-pipes

I'm trying to use a combination of purescript-pipes, and purescript-pipes-aff to write a version of await which will return Nothing if it doesn't receive a value in a specified amount of time. So far, I've written the following: timeOut :: forall a…
Joe
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Parsing an iterable without listifying each chunk

Suppose I want to achieve a splitting of a Python iterable, without listifying each chunk, similar to itertools.groupby, whose chunks are lazy. But I want to do it on a more sophisticated condition than equality of a key. So more like a parser. For…
Eric Auld
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"Yield from" in Haskell Pipes

In Haskell Pipes, suppose I am writing f :: Producer a m () and I am inside a do block with respect to m (Edit: this doesn’t make sense; I want a producer do block). Inside this do block, I want to yield from g :: Producer a m () before returning to…
Eric Auld
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Pipes `run` with State

I have a producer: p :: Producer Message IO r. I can process all messages using: runEffect $ for p processMessage where processMessage :: Message -> Effect IO (). How can I implement stateful processing using something like: processMessage ::…
krokodil
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how to insert an IO operation into a Pipe

I have a Haskell function which given a directory from which to get recursively all files and writes the filenames into a file. This is a simple example to start with. In the next step I must replace the mapping from file to a text (the transf…
user855443
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How to write GroupBy function using the Pipes library

I've figured out a way to implement this function on the InCore representation of the data as follows: groupByCol :: (Eq a, Ord a, RecVec rs) => (forall (f :: * -> *). Functor f => (a -> f a) -> Record…
josiah
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How to use a ZMQ subscriber in Haskell with pipes

I can get a ZMQ subscriber to work in Haskell, but would appreciate guidance on how to use that data with Pipes. My attempt at writing a Producer fails at 'stack build' with the following error: Couldn't match type ‘Proxy X () c'0 c0 (ZMQ z)’ with…
Stuart
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GroupBy of stream by agreggateId (Haskell / concurrency streaming)

Context : I'm implementing an App in CQRS and I'm trying to optimize the processing of commands (1 stream by aggregate Id basically)... Problem : I would like to have a first stream that receives all the commands and dispatches these ones by their…
Nicolas Henin
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Reading strings from stdin or argument in Haskell CLI

I'm trying to build a Haskell CLI that can either read in strings from stdin or from arguments like so: cat colors-multi-line | colorshift -d 10 colorshift -d 10 "#FFFFFF" How would I accomplish this?
Carolyn Knight-Serrano
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Turtle: dealing with non-utf8 input

In my path to learning Pipes, I've run into problems when dealing with non-utf8 files. That is why I've took a detour into the Turtle library to try to understand how to solve the problem there, at higher level of abstraction. The exercise I want to…
Damian Nadales
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