- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] How to turn Integer into Proxy (n :: KnownNat) with n equal to the integer?
by Johannes Waldmann 16 Aug '18

16 Aug '18

> How can I convert an Integer into a Proxy (n :: KnownNat) > with n equal to the integer? Data.Reflection.reifyNat ? https://mail.haskell.org/pipermail/haskell-cafe/2017-November/128152.html - J.W.

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A function synonym is not (by default) as polymorphic as the original.
by Jeffrey Brown 15 Aug '18

15 Aug '18

Today I was writing a lot of Hashable instances, and found it hard to read code littered long lines mostly consisting of `hashWithSalt`, so I made a synonym: infixl 5 ## (##) = hashWithSalt But when I replaced all the `hashWithSalt`s with ##, I got lots of weird errors -- GHC kept wanting things to be Strings that were Ints, or vice verse. The problem vanished when I added this type signature: (##) :: Hashable a => Int -> a -> Int That's exactly the same type signature that hashWithSalt has. Is this expected behavior? Desirable? -- Jeff Brown | Jeffrey Benjamin Brown Website <https://msu.edu/~brown202/> | Facebook <https://www.facebook.com/mejeff.younotjeff> | LinkedIn <https://www.linkedin.com/in/jeffreybenjaminbrown>(spammy, so I often miss messages here) | Github <https://github.com/jeffreybenjaminbrown>

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Status of the Hi Haddock project
by Simon Jakobi 14 Aug '18

14 Aug '18

Hi! I have summarized the status of my GSoC project at https://sjakobi.github.io/blog/2018/08/14/hi-haddock-3/ My WIP patches for GHC and haddock are at https://phabricator.haskell.org/D5067 and https://github.com/haskell/haddock/pull/906. Cheers, Simon

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Is there a library that has a strict version of `sum`?
by Damian Nadales 14 Aug '18

14 Aug '18

I thought the answer would be easy to find on the internet, but I cannot find any package that features a strict version of `sum`. Do you know if such a function is defined anywhere? (like a custom prelude for instance) I know it is trivial to define, but I would prefer not to repeat myself (and somebody else). Thanks!

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First Call for Participation for IFL 2018 (Implementation and Application of Functional Languages)
by Jurriaan Hage 14 Aug '18

14 Aug '18

Hello, Please, find below the 1st call for participation for IFL 2018. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL --- CALL FOR PARTICIPATION: ================================================================================ IFL 2018 30th Symposium on Implementation and Application of Functional Languages University of Massachusetts Lowell, MA, USA September 5th-7th, 2018 http://iflconference.org September 5th: Haskell Mini-Course by Galois, Inc, see details below. ================================================================================ ### Scope The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2018 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. ### Keynote Speakers * Adam Chlipala, Massachusetts Institute of Technology CSAIL * Arjun Guha, University of Massachusetts Amherst ### Haskell Mini-Course (September 5th, 2018) Mini-course on Haskell by Galois, Inc, presented by David Thrane Christiansen and Jose Manuel Calderon Trilla. Register: Attendance at the course is free, but you must RSVP. (Link to RSVP form can be found at http://iflconference.org) Course Description: Recent versions of the GHC compiler for Haskell feature support for a number of advanced type system features, including pattern-matching functions in the type system (type families), indexed families (generalized algebraic datatypes, or GADTs), type-level data structures (data kinds), and general compile-time metaprogramming (Template Haskell). At Galois, we use these features in a number of our projects, which allows us to build deep embeddings of programming languages and have GHC enforce the target language's type system for us. This style of programming ensures that we only produce well-typed terms, including that we do not forget any of the run-time checks that are necessary to preserve our invariants when accepting input from untyped sources such as files. In the course of developing these projects, some common problems and programming patterns emerged. We developed the `parameterized-utils` library to codify solutions to these problems, and provide necessary generalizations of interfaces from the standard library (Eq, Applicative, Traversable, etc.) We will expect that participants in the course have used Haskell before, but we will not expect everyone to be experts. We will introduce GADTs, type families, and data kinds, and then show how to use them together with the tools from parameterized-utils with an implementation of the simply-typed lambda calculus, including basic AST definitions, evaluation, and parsing. ### Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honored article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. ### Organization and Program committee Chairs: Jay McCarthy & Matteo Cimini, University of Massachusetts Lowell, USA Program Committee: * Arthur Chargueraud, Inria, FR * Ben Delaware, Purdue University, USA * Christos Dimoulas, Northwestern University, USA * David Darais, University of Vermont, USA * Dominic Orchard, University of Kent, UK * Ekaterina Komendantskaya, Heriot-Watt University, UK * Garrett Morris, University of Kansas, USA * Heather Miller, EPFL & Northeastern University, CH & USA * Jeremy Yallop, University of Cambridge, UK * Keiko Nakata, SAP Innovation Center Potsdam, DE * Laura Castro, University of A Coruna, ESP * Magnus Myreen, Chalmers University of Technology, SWE * Natalia Chechina, Bournemouth University, UK * Peter Achten, Radboud Universiteit Nijmegen, NL * Peter-Michael Osera, Grinnell College, USA * Richard Eisenberg, Bryn Mawr College, USA * Trevor McDonell, University of New South Wales, AUS * Yukiyoshi Kameyama, University of Tsukuba, JAP ### Venue The 30th IFL is organized by the University of Massachusetts Lowell. The City of Lowell is located at the heart of the Merrimack Valley just 30 miles northwest of Boston. Lowell can be easily reached by train or taxi. See the website for more information on the venue.

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What is the right way to use unsafeCoerce?
by Cosmia Fu 14 Aug '18

14 Aug '18

Hi all, I have noticed that unsafeCoerce is able to > Prelude> import Unsafe.Coerce > Prelude Unsafe.Coerce> data P = P Int Double deriving Show > Prelude Unsafe.Coerce> data Q a b = Q a b deriving Show > Prelude Unsafe.Coerce> unsafeCoerce (P 23 2.33) :: Q Int Double > Q 23 2.33 And it works even for sum type, and the first constructor always wins. > Prelude Unsafe.Coerce> data M a = J a deriving Show > Prelude Unsafe.Coerce> unsafeCoerce (J "qwe") :: Either String String > Left "qwe" > Prelude Unsafe.Coerce> unsafeCoerce (Just "qwe") :: M String > J "qwe" And the documenation for unsafeCoerce# says > Casting between two types that have the same runtime representation. One case is when the two types differ only in "phantom" type parameters, for example Ptr Int to Ptr Float, or [Int] to [Float] when the list is known to be empty. Also, a newtype of a type T has the same representation at runtime as T. > http://hackage.haskell.org/package/base-4.11.1.0/docs/GHC-Exts.html#v:unsaf… But info tables for different constructors are different. Why does the code above work? And is it safe to use unsafeCoerce like this? Thanks, Cosmia Fu

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Learning & Haskell Job Board
by Alex Mesropians 13 Aug '18

13 Aug '18

Hey All, Just wanted to share Workshub <http://t.sidekickopen13.com/e1t/c/5/f18dQhb0S7lC8dDMPbW2n0x6l2B9nMJW7t5XZs5…> with you all for those looking to hire Haskell engineers or want to see for yourself whats out there! We also have a learn section which is forever growing with new FP related content! We are always also looking for people to contribute to! thanks, Alex

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Google Summer of Code : CodeWorld
by Krystal Maughan 13 Aug '18

13 Aug '18

Hi All, I wrote a blog post on features I worked on this summer for Google Summer of Code in CodeWorld. Hope you enjoy it! Thank you for giving me the opportunity to work in Haskell this summer! https://medium.com/@krystal.maughan/breaking-the-space-time-barrier-with-ha… Best, Krystal

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cpphs broken on GHC 8.6.1
by Vanessa McHale 13 Aug '18

13 Aug '18

As of the latest release of GHC 8.6.1, cpphs no longer compiles. Anyone happen to know what's going on? Thanks! -- *Vanessa McHale* Functional Compiler Engineer | Chicago, IL Website: www.iohk.io <http://iohk.io> Twitter: @vamchale PGP Key ID: 4209B7B5 Input Output <http://iohk.io> Twitter <https://twitter.com/InputOutputHK> Github <https://github.com/input-output-hk> LinkedIn <https://www.linkedin.com/company/input-output-global> This e-mail and any file transmitted with it are confidential and intended solely for the use of the recipient(s) to whom it is addressed. Dissemination, distribution, and/or copying of the transmission by anyone other than the intended recipient(s) is prohibited. If you have received this transmission in error please notify IOHK immediately and delete it from your system. E-mail transmissions cannot be guaranteed to be secure or error free. We do not accept liability for any loss, damage, or error arising from this transmission

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hs-boot and (micro)lenses
by Francesco Ariis 12 Aug '18

12 Aug '18

Hello cafe, I have some problem setting up an appropriate .hs-boot module. I attach a .tar.gz'd cabal folder, so you can immediately test it with `cabal new-repl`. I had a file like this -- datatypes data A = A { _i :: Int, _b :: B } type AS a = State A a data B = B (AS ()) makeLenses ''A -- functions f :: B f = B $ i .= 18 So I decided to split it up in 2 files to test hs-boot in the wild: -- A.hs ------- data A = A { _i :: Int, _b :: B } type AS a = State A a makeLenses ''A -- B.hs ------- data B = B (AS ()) f :: B f = B $ i .= 18 Well, I don't know how to write A.hs-boot. I tried this: module A where import Lens.Micro.Platform data A b :: Lens' A B but ghc rightfully complains that he doesn't know about B, and if I slap an `import B` in the .hs-boot then I have another import-cycle. What's the way out of that? The project I am dealing with is bigger than this problem and I would really love to keep functions and related datatypes nearby for mental sanity. As I wrote above, attached you can find a .tar.gz with everything set up to replicate this -F

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