July 2019 - Haskell-Cafe

Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 191, Issue 5
by Information The FLOSS 10 Jul '19

10 Jul '19

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The GHC Committee welcomes its new members
by Joachim Breitner 10 Jul '19

10 Jul '19

Dear Haskell community, the GHC Steering committee welcomes its new two members, Sandy Maguire and Arnaud Spiwack. We are happy to see that there is continued interest in our work, and are looking forward to the insights and energy that are brought to the committee by Sandy and Arnaud. They take the seats of Ben Gamari and Manuel Chakravarty. A big thanks to Ben and Manuel for their contributions to GHC and the proposal committee. In particular Ben, who created the initials draft of the proposal process. We had four nominations in total, and I would like to preserve their privacy. Since we only had two seats to fill, we had to make a pick; nevertheless I am grateful for all nominations, and encourage everyone, including those who did not make it this time, to try again next time. Neither the committee nor its process is perfect, as the way two recent proposals went show, but we are constantly trying to refine and improve. Your feedback is always welcome, either at the committee mailing list, or in private communication with the Chairs (the two Simons), me, or any other member. On behalf of the committee, Joachim Breitner PS: Sandy and Arnaud, please subscribe to the mailing list at https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee -- Joachim Breitner mail(a)joachim-breitner.de http://www.joachim-breitner.de/

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mapM and Control.Arrow
by Olaf Klinke 09 Jul '19

09 Jul '19

Dear cafe, consider the declaration mapM :: (SomeArrow a, Traversable t) => a b c -> a (t b) (t c) For the Arrow a = (->), the above mapM is just an over-constrained fmap, since Functor is a superclass of Traversable. For the arrow a = Kleisi m, the above mapM is the Control.Monad.mapM we know. Currently I fail to see how it could be defined with any of the existing sub-classes in Control.Arrow. One might say that fmap and mapM are on the same spectrum: If you specialize SomeArrow to (->) you can generalize Traversable to Functor, if you specialize Functor to Traversable you can generalize (->) to SomeArrow. Cheers, Olaf

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Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 191, Issue 4
by Information The FLOSS 09 Jul '19

09 Jul '19

Bu ileti The FLOSS Information'a gönderdiğiniz ileti sonucunda otomatik olarak oluşturuldu. Bu iletiye yanıt vermenize gerek yoktur. Bu iletiyi gönderdiğiniz için teşekkür ederiz. 4 gün içerisinde yanıtlamaya çalışacağız. Eğer 4 gün içinde yanıt gelmezse tekrar ileti gönderebilirsiniz. Sık Sorulabilecek Sorular: https://theflossinformation.gitlab.io/sik-sorulabilecek-sorular.html Hakkımızda: https://theflossinformation.gitlab.io/hakkimizda.html Bize Ulaşın: https://theflossinformation.gitlab.io/bize-ulasin.html Saygılarımızla, The FLOSS Information https://theflossinformation.gitlab.io/

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parallel Haskell with limited sparks
by Henning Thielemann 09 Jul '19

09 Jul '19

When I read about parallel programming in Haskell it is always about manual chunking of data. Why? Most of my applications with parallelization benefit from a different computation scheme: Start a fixed number of threads (at most the number of available computing cores) and whenever a thread finishes a task it gets assigned a new one. This is how make -j, cabal install -j, ghc -j, work. I wrote my own package pooled-io which does the same for IO in Haskell and there seem to be more packages that implemented the same idea. Can I have that computation scheme for non-IO computations, too? With Parallel Strategies, monad-par etc.?

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{-# SPECIALIZE foo @Bar #-} ?
by Johannes Waldmann 08 Jul '19

08 Jul '19

Dear Cafe, with pragma SPECIALIZE, I find it tedious to repeat the type declaration. (It's a burden for maintenance and readability.) Could we use type-application syntax instead? E.g., the example from here https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_ext… hammeredLookup :: Ord key => [(key, value)] -> key -> value {-# SPECIALIZE hammeredLookup :: [(Widget, value)] -> Widget -> value #-} would become hammeredLookup :: forall key value . Ord key => [(key, value)] -> key -> value {-# SPECIALIZE hammeredLookup @Widget #-} or {-# SPECIALIZE hammeredLookup @Widget @value #-} Cf. SPECIALIZE instance, where we already write the instantiation for the type variable(s). - J.W.

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Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 191, Issue 3
by Information The FLOSS 08 Jul '19

08 Jul '19

Bu ileti The FLOSS Information'a gönderdiğiniz ileti sonucunda otomatik olarak oluşturuldu. Bu iletiye yanıt vermenize gerek yoktur. Bu iletiyi gönderdiğiniz için teşekkür ederiz. 4 gün içerisinde yanıtlamaya çalışacağız. Eğer 4 gün içinde yanıt gelmezse tekrar ileti gönderebilirsiniz. Sık Sorulabilecek Sorular: https://theflossinformation.gitlab.io/sik-sorulabilecek-sorular.html Hakkımızda: https://theflossinformation.gitlab.io/hakkimizda.html Bize Ulaşın: https://theflossinformation.gitlab.io/bize-ulasin.html Saygılarımızla, The FLOSS Information https://theflossinformation.gitlab.io/

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Call for Participation: Summer BOB 2019 (August 21, Berlin)
by Stefan Wehr 08 Jul '19

08 Jul '19

======================================================================== Summer BOB 2019 Conference “What happens if we simply use what’s best?” August 21, 2019, Berlin co-located with ICFP 2019 http://bobkonf.de/2019-summer/ Program: http://bobkonf.de/2019-summer/program.html Registration: http://bobkonf.de/2019-summer/registration.html ======================================================================== Are you interested in technologies beyond the mainstream, that are a pleasure to use, and effective at getting the job done? BOB is the forum for developers, architects and builders to explore and discover the best tools available today for building software. Our goal is for all participants to leave the conference with new ideas to improve development back at the ranch. Summer BOB is a one-time-only event, in the spirit of the spectacular Winter BOB. The International Conference on Functional Programming is coming to town, and Summer BOB will be right in the middle of it, on the last day of ICFP proper, prior to all the workshops. Summer BOB will feature two tracks: one from practitioners, and one from researchers, and foster communication and cross-pollination between these communities. BOB features two tracks of seven talk each: One research track with invited talks, and one track by practitioners, designed to cross-pollinate and inspire. http://bobkonf.de/2019-summer/program.html Topics include distributed programming, testing, linear algebra, functional design patterns, type systems, formal methods, and interactive development. We are committed to diversity: We aim at exploring a wide range of tools in a welcoming and friendly crowd of diverse people. To that end, a number of support options for participants from groups under-represented in tech are available. http://bobkonf.de/2019-summer/registration.html NOTE: The early-bird rates expire on July 18, 2019!

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Help wanted getting old GADT code to compile
by nr＠cs.tufts.edu 05 Jul '19

05 Jul '19

Here is a legacy file that does not compile with GHC 8.0.1: {-# LANGUAGE RankNTypes, GADTs, KindSignatures #-} module Bookgadt where data TExp :: * -> * where TLit :: (forall a . (a -> (TExp a))) TLit' :: (a -> (TExp a)) The compiler rejects value constructor TLit with this error message: • Data constructor ‘TLit’ returns type ‘forall a. a -> TExp a’ instead of an instance of its parent type ‘TExp a’ I really want to keep the explicit "forall," as I'm trying to make a point for readers not familiar with Haskell. Does anyone know if there is some option or other incantation that would enable this code to compile? Norman

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The future of the SPARC NCG backend
by Ben Gamari 01 Jul '19

01 Jul '19

Hello everyone, If you use (or think you might use in the future) GHC's SPARC NCG backend please do leave a note on #16882 [1]. My impression is that it has no users and no plausible means of testing. Consequently I am suggesting that we remove it in GHC 8.12. Cheers, - Ben [1] https://gitlab.haskell.org/ghc/ghc/issues/16882

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