- Haskell-Cafe - Haskell.org

Cleanup obsolete stack stuff (compiler, libraries, etc.)
by Geraldus 06 Feb '17

06 Feb '17

Hi folks! I want to perform some cleanup deleting obsolete compilers located in ~/.stack folder. I know stack places them into ~/.stack/programs/<platform>/ directory, however I think there are also should be something else related, e.g. docs and libs, and especially packages that was built when I used old LTS snapshots. What is the best way to perform such cleanup?

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Removing Hackage packages
by aditya siram 05 Feb '17

05 Feb '17

Hi, I'd like to remove a couple of my packages [1] from Hackage. How do I do that? Thanks! -deech [1] http://hackage.haskell.org/package/fltkhs-demos, http://hackage.haskell.org/package/fltkhs-fluid-demos

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ghci, running :load on filename provided by variable
by Dennis Raddle 04 Feb '17

04 Feb '17

How do I load a file in ghci where the filename comes from a variable? So like, let f = "myfile.hs" :load f D

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Getting added to the Haskell group on Github.
by aditya siram 04 Feb '17

04 Feb '17

Hi, Some time ago the maintainership of c2hs [1] was silently passed to me. However I am unable to request access to the repo because I am not on the Haskell team [2]. Apparently I have to be added by someone already on the team but I'm having trouble getting in touch with someone. If anyone reading this is on the team [2] please add me. I'm @deech on Github. Thanks! -deech [1] https://github.com/haskell/c2hs [2] https://github.com/orgs/haskell/people

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Purpose of Control.Monad.Base class
by Guru Devanla 04 Feb '17

04 Feb '17

Hello, I am trying to understand the purpose of the MonadBase class. https://hackage.haskell.org/package/transformers-base-0.4.4/docs/Control-Mo… Google search did not give me any helpful answers. Please could some one help me understand the purpose of this class and also point me to any good resources. Thanks Guru

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using ghci with compiled code
by Dennis Raddle 04 Feb '17

04 Feb '17

I want to use ghci to interpret parts of my program, and I would like it to pick up pre-compiled object files to speed things up in other parts. Right now whenever I launch ghci it seems to "compile" everything (I think to byte code).. what can I do? D

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Best way to provide monad transformer instances in library design?
by Matt 03 Feb '17

03 Feb '17

I'm writing a wrapper around ekg which provides an MTL-style class for recording metrics [1], and now I'm trying to figure out how to make the class usable for clients. I'm conflicted on the numerous ways to approach the problem. I would like to provide the best UX for the library, and want to consider viewpoints other than my own. Currently, the class is: class MonadMetrics m where getMetrics :: m Metrics I currently don't provide any concrete transformer, instead requiring that users define it for their own stacks. I'd like to make it easier to use. I can provide a concrete transformer newtype MetricT m a = MetricT (ReaderT Metrics m a) instance Monad m => MonadMetrics (MetricT m) where getMetrics = MetricT ask and then provide a wide variety of pass through instances. This approach requires a large amount of boilerplate, and for any instances I forget to provide, will require that clients make their own orphan instances. It also incurs additional dependencies just for writing instances. I can provide a more abstract transformer and a more general Metrics class: class HasMetrics r where metrics :: Lens' r Metrics newtype MetricT2 m a = MetricT2 (m a) instance (MonadReader r m, HasMetrics r) => MonadMetrics (MetricT2 m) where getMetrics = MetricT (view metrics) but this still requires those pass through instances. Finally, I can scrap `MonadMetrics` as anything other than a class alias: class (MonadReader r m, MonadIO m, HasMetrics r) => MonadMetrics r m instance (MonadReader r m, MonadIO m, HasMetrics r) => MonadMetrics r m but now I have UndecidableInstances and a multiparam type class, and I'm not sure how well this actually plays out in the wild. What are your thoughts on this issue? Matt Parsons [1]: https://github.com/sellerlabs/monad-metrics

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segfault with Hint (InterpreterT)
by Dennis Raddle 03 Feb '17

03 Feb '17

My program segfaults the second time it run runInterpreterT. Just wondering if that's not supposed to be allowed. I'm actually not sure what triggers the segfault -- it's also doing some MIDI I/O. D

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is there less available support for beginners these days?
by Dennis Raddle 03 Feb '17

03 Feb '17

I'm a Haskell hobbyist enthusiast -- first learned it in 2008, struggling having come from an imperative language background, and I only get to use it in hobby projects, but I love it more each year. I still consider myself a beginner in many areas. Unfortunately it used to be much easier to get responses on the beginner's list or the #haskell channel. I've now had several posts go completely unanswered on the beginner's list, and can't get help from #haskell most of the time (by "help" I mean someone who takes just a few minutes with me). I've tried posting on Haskell cafe in the hopes I would get more responses and I'm not sure if that's going to work (or is appropriate). D

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Project hosting platform - looking for new developer
by fr33domlover 03 Feb '17

03 Feb '17

(tl;dr Git and Darcs hosting platform with planned federation written in Yesod, I'm looking for someone excited about the idea to take over development) Hello Haskellers, Several months ago I started developing a project hosting platform called Vervis. It's written in Haskell using the Yesod web framework. The intention was to make it federated and allow people for the first time in git (and darcs) history to enjoy both the full access to the community and avoid the proprietaryness and centralization of githu8. I'm probably still really a beginner and I never made any web application before Vervis, or even an actual mature stable software project. But I made huge progress with Vervis very fast, and I created something you can actually see with your eyes :) However due to certain life preferences I stopped working on it and I may never go back to it. But I was hoping someone else would want to continue its development. The code is hosted both at Darcs Hub and in a Vervis instance, so the project is self-hosting: https://dev.seek-together.space/s/fr33domlover/r/vervis I didn't work on design much, just focused on functionality. Among the unique features already present one one way or another: - Supports both Git and Darcs - Rendering of documents using Pandoc, supporting more formats and variants than any other platform could - Support of Libravatar for user avatar images - Flexible integrated system for project management and issues, on the level you can find in project management platforms, but here it's integrated into the code hosting platform itself - Hierarchical discussion threads - A single project can contain more than one repo, i.e. repos can share the same project plan and the same issue database - Merely being written in Haskell and Yesod makes it very stable once it builds successfully There are still many quirks, including the UI of the registration system and UI in general, so I'm sorry in advance if you try to create an account there and get errors or confusing UIs. It's not polished or anything yet. I also made several support projects and implemented some helper tools, such as some support for parsing darcs repos (attoparsec stuff that can and maybe should be merged into Darcs itself), SSH server component that uses an improved version of the ssh package, hierarchical SQL query API with an interface similar to the FGL library, code for working with git repos... and probably more things I'm forgetting. If you have any questions, I'm here to answer :) --fr33

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