October 2019 - Haskell-Cafe

Using GHCJS on firebase functions
by Ruben Astudillo 15 Oct '19

15 Oct '19

Dear list Has anyone used GHCJS on Firebase functions? How has it been your experience? Would you recommend it or offer al alternative?. -- -- Ruben -- PGP: 4EE9 28F7 932E F4AD

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Avoiding code-duplication for what is roughly fmap
by Sebastiaan Joosten 15 Oct '19

15 Oct '19

Hi all, I'm writing a lot of code that looks like this: instance WhiteSpaced ClassItem where removeWS (Method a b c) = Method (removeWS a) (removeWS b) (removeWS c) removeWS (Declaration b) = Declaration (removeWS b) Typically, all the way at the end there's an instance that deviates (sometimes the deviating instances are somewhere in the middle). I need to do this for a lot of functions, and a lot of data types, and all I'm doing here is rewriting the data-type declaration in a different syntax (except that you do not know the types of a, b and c from the above). For the sake of maintainability, I want to avoid this code-duplication and focus only on the deviating instances. How to do better? I don't see how to use generics (in the hope of only writing 'instance WhiteSpaced ClassItem where' instead of the three lines above) for this: the types for a, b and c are all different here. Would this be easier with Template Haskell? (in the hope of only writing $(''something ClassItem) instead of the three lines above) My main concern is maintainability, an ideal solution is either a clear one-liner or a library import (in the same way that aeson allows me to use generics or Template Haskell without needing to know much about them). Other solutions are welcome too. Best, Sebastiaan

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Re: [Haskell-cafe] Is join useful for every monad?
by Ruben Astudillo 14 Oct '19

14 Oct '19

On 14-10-19 16:45, Carter Schonwald wrote: > And while join is not at the moment in the Monad typeclass because of > newtype stuff Could you expand a bit on this? I remember this being on a Applicative-Monad proposal but I couldn't understand why it wasn't technically possible. -- -- Ruben -- PGP: 4EE9 28F7 932E F4AD

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[Job] Muse Dev, a Galois spin-out, is hiring
by Thomas DuBuisson 14 Oct '19

14 Oct '19

Muse Dev is a Galois spin-out working to put the rest of Galois out of business by automating their jobs away [1]. By discovering "the right issues at the right time" and presenting to the developer, Muse seeks to bring static code analysis to the world as early in the development cycle as possible. We're currently working with early adopters to flesh-out the interface and add final must-haves. Oh, and we are hiring. If you like all-Haskell backends, have SaaS-related experience, and love build systems then please apply. We're interested in people with experience and enthusiasm in some of: * Haskell development * Static analysis * Build system interpretation * Kubernetes cluster deployment * AWS such as EC2, IAM, EKS * REST APIs * Enterprise system deployment, packaging, and support Location: Galois offices in Portland, Oregon or Arlington, Virginia. Resumes can be sent to careers(a)muse.dev See Also https://muse.dev <https://muse.dev/careers> https://lifeatgalois.com - We have inherited some culture from Galois but are a separate company. [1] Well, anything that can be automated about program analysis. Don't tell Galois. They'll kick us out of this nice, comfy, office.

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Optional "Default" instances of classes in certain subcases (but too broad)
by Juan Casanova 14 Oct '19

14 Oct '19

Hello again, Before my question, I notice I am using this list quite a bit. I hope I am no abusing or misusing it by doing so, though. Sometimes I wonder what's the line between what I should ask here and what I should ask in StackOverflow, if that line even exists. If anyone feels I may be abusing or misusing, please let me know (in public or in private). Very simple question: Would it make sense, or does it already exist, a way to implement *optional* default instances of classes that can be used more directly than currently. I am *not* talking about providing a default implementation of a class when declaring it. I know you can do this. I am talking about when you know you can provide a generic instance of a class for a wide range of situations *which depends on some constraints*. For example: instance Bifunctor f => Functor (f a) where fmap = bimap id Of course, this is a terrible idea, because the constraints are not checked when verifying overlap and the like, and so this is very likely to break your program. What I tend to do nowadays is to add a function: fmapFromBiMap :: Bifunctor f => (b -> c) -> (f a b) -> (f a c) fmapFromBiMap = bimap id and then use it each time (the following is obviously a silly example): instance Functor (Either a) where fmap = fmapFromBiMap The only problem I see with this is that I need to remember (specially with my own type classes): 1. That I provided this "default" implementation. 2. Its name. I know these are fairly small things to complain about, but once again when you do it 100 times it becomes annoying, specially for a person who absolutely does not like doing things that I know would be able to explain how to automate. So, what I would expect is for it to be something like declaring the default instance but only use it for the types that explicitly ask for it. E.g.: optional instance Bifunctor f => Functor (f a) where fmap = bimap id instance Functor (Either a) using optional The main important point here is that I expect this to check the constraints in compile time for the class that I am giving (and if it contains type variables, only use those that are guaranteed to be complied, of course). This means that if I did: instance Functor (f a) using optional I *do not* expect it to be okay with it and automatically add the constraint Bifunctor f => to the instance. I expect it to give me a compile error: "No matching optional instance found". Of course, there could be several optional instances that overlap when using optional. But then, GHC would give me the error indicating what the options are *and I would know that it's because I put optional* and I could just replace it with the specific one to use. Maybe by giving them names? optional instance fmapFromBiMap Bifunctor f => Functor (f a) where fmap = bimap id instance Functor (Either a) using optional -- If this does not work because it overlaps with other optionals, then GHC tells me, indicates the options, and I replace with: instance Functor (Either a) using fmapFromBiMap This avoids the problem of defining the instance in general (that it will overlap with basically anything), should be easy to type check and prevents having to keep an index in your mind about useful functions that you implemented or didn't. I wonder if the "deriving" family of functionalities have anything like this, but my search has not been fruitful. Maybe using Generics? Maybe I just need good autocomplete so that I can find the function easily... it still feels like this would make sense. Juan. -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.

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Feedback First Application
by Casper Thule Hansen 14 Oct '19

14 Oct '19

Hi. I have created my first application that I expect will go live within the next couple of months and I would like to have some feedback. The application is here: https://github.com/into-cps-association/utilities_backend and will be a project that I keep updating as I learn new stuff. I consider myself somewhat a haskell beginner, and my goal is to learn more about Haskell's features, packages and similar. So I hope that someone can point me to some places in my code that can be written in a better fashion, concepts that can be applied or similar. Of course - please try to keep it within my reach 🙂 The application is not critical in any fashion. It is not necessary with optimal performance, extensive testing and similar. Currently, I am not particularly interested in testing, I will save that for later. I hope someone can give me a few pointers! Cheers, Casper Thule

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Twitter-conduit author not responding
by Corentin Dupont 12 Oct '19

12 Oct '19

Hi community, I have a small problem with the "Twitter-conduit" package: https://github.com/himura/twitter-conduit Their are several opened issues and pull requests, in particular the Twitter API changed so the package is relatively broken. I mailed the author some month ago, without response. What is the recommended course of action? Regards Corentin

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[TFP'20] one month left for pre-symposium submissions for Trends in Functional Programming 2020, 13-14 February, Krakow, Poland
by Peter Achten 11 Oct '19

11 Oct '19

------------------------------------------------------------------------- Second call for papers 21st Symposium on Trends in Functional Programming tfp2020.org ------------------------------------------------------------------------- The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions. * TFP is moving to new winter dates, to provide an FP forum in between the annual ICFP events. * TFP offers a supportive reviewing process designed to help less experienced authors succeed, with two rounds of review, both before and after the symposium itself. Authors have an opportunity to address reviewers' concerns before final decisions on publication in the proceedings. * TFP offers two "best paper" awards, the John McCarthy award for best paper, and the David Turner award for best student paper. * This year we are particularly excited to co-locate with Lambda Days in beautiful Krakow. Lambda Days is a vibrant developer conference with hundreds of attendees and a lively programme of talks on functional programming in practice. TFP will be held in the same venue, and participants will be able to session-hop between the two events. Important Dates --------------- Submission deadline for pre-symposium review: 15th November, 2019 Submission deadline for draft papers: 10th January, 2020 Symposium dates: 13-14th February, 2020 Visit tfp2020.org for more information.

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Hiring Using Opensource? - Haskell Community
by Alex Mesropians 10 Oct '19

10 Oct '19

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Hedgehog: returning a list from `commandExecute` and getting to the items in an update function
by Magnus Therning 10 Oct '19

10 Oct '19

Hello, I'm trying to use Hedgehog to test a web app at work. Yesterday I ran into an issue with getting to the value returned from my `commandExecute` in an `Update` `Callback`. Basically my model looks like this ~~~ newtype State (v :: * -> *) = State (M.Map (Var UUID v) DataPerItem) deriving (Eq, Show) ~~~ and I have an action, `Command gen exec [Update update]` where ~~~ exec :: action -> m [UUID] ~~~ which results in ~~~ update :: State v -> action -> Var [UUID] v -> State v ~~~ AFAICS I need to, in order to actually update my model, turn that `Var [UUID] v` into `[Var UUID v]`. I've been staring at the functions in Hedgehog for a while now but nothing jumps out... or am I, once again, thinking about it all wrong? :) /M I also asked at stackoverflow: https://stackoverflow.com/questions/58157292/returning-a-list-and-getting-t… This is just to widen the net a bit... -- Magnus Therning OpenPGP: 0x927912051716CE39 email: magnus(a)therning.org twitter: magthe http://magnus.therning.org/ Ah, good taste! What a dreadful thing! Taste is the enemy of creativeness. — Pablo Picasso

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