- Glasgow-haskell-users

Re: Proposal: Turn on ScopedTypeVariables by default
by Roman Cheplyaka 24 Feb '15

24 Feb '15

On 24/02/15 14:46, Herbert Valerio Riedel wrote: > On 2015-02-23 at 18:45:20 +0100, David Feuer wrote: >> I know this will be controversial, because it can break (weird) code and >> because it's not Haskell 2010, but hey, you can't make brain salad without >> breaking a few heads. > > Are you suggesting enabling -XScopedTypeVariables for -XHaskell98 and > -XHaskell2010? or rather for the default when neither of those two modes > is explicitly requested? > > Just be warned though: this is somewhat of a trick-question... :-) Maybe in addition to -XHaskell98 and -XHaskell2010 there should also be -XGhcHaskell. ghc already deviates from the standard by default (e.g. -XNondecreasingIndentation). OTOH we probably don't want end up with -fglasgow-exts once again. Roman

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Proposal: Turn on ScopedTypeVariables by default
by David Feuer 23 Feb '15

23 Feb '15

I know this will be controversial, because it can break (weird) code and because it's not Haskell 2010, but hey, you can't make brain salad without breaking a few heads. ScopedTypeVariables is just awesome for two fundamental reasons: 1. It lets you write type signatures for more things. 2. It lets you write more precise type signatures for many things. As a consequence of those two, 3. It helps you get much better error messages from the type checker. And for all that, 4. It's really easy to use. What do other people think?

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ANNOUNCE: GHC 7.10.1 Release Candidate 2
by Austin Seipp 21 Feb '15

21 Feb '15

We are pleased to announce the second release candidate for GHC 7.10.1: https://downloads.haskell.org/~ghc/7.10.1-rc2/ This includes the source tarball and bindists for 64bit/32bit Linux and Windows. Binary builds for other platforms will be available shortly. (CentOS 6.5 binaries are not available at this time like they were for 7.8.x). These binaries and tarballs have an accompanying SHA256SUMS file signed by my GPG key id (0x3B58D86F). We plan to make the 7.10.1 release sometime in February of 2015. Please test as much as possible; bugs are much cheaper if we find them before the release! -- Regards, Austin Seipp, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/

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type checker plugin success depends on whether an expression is manually inlined
by adam vogt 20 Feb '15

20 Feb '15

Hello list, The following file compiles with my plugin. It makes a data family HList have role representational in a way that I believe is safe: https://github.com/aavogt/HListPlugin/blob/master/ex/Coerce.hs#L19 I expect the highlighted line to be acceptable. However, it seems that the plugin never sees anything from line 19, when I uncomment it. Is there something I can do to make that L19 work? Is this a known or intentional limitation of type checker plugins? Thanks, Adam

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ApplicativeDo
by Thomas Bereknyei 19 Feb '15

19 Feb '15

There is a library for TH: http://hackage.haskell.org/package/applicative-quoters-0.1.0.8 (broken at the moment) There is a proposal at: https://ghc.haskell.org/trac/ghc/wiki/ApplicativeDo Now with AMP, is this worth revisiting? Why or why not? -Tom

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Re: ANNOUNCE: GHC 7.10.1 Release Candidate 2
by Takenobu Tani 17 Feb '15

17 Feb '15

Hi Herbert, Thank you for your directions. I will send the pull-request after checking the file. Thank you, Takenobu 2015-02-17 22:02 GMT+09:00 Herbert Valerio Riedel <hvriedel(a)gmail.com>: > On 2015-02-17 at 13:47:50 +0100, Takenobu Tani wrote: > > I modified System/Process/Internals.hs locally and build on MinGW 32bit. > > Then I was successful to build on 32bit Windows 7. > > > > Shall I write a bug report on trac or any? or ghc7.10.1.rc2 will not > > support 32 bit Windows? > > Please file a pull-request at https://github.com/haskell/process > > I'm somewhat surprised this wasn't noticed before(?) >

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type checker plugin does not affect inferred type signatures
by adam vogt 16 Feb '15

16 Feb '15

Hello, Using ghc-7.10 rc1, I am trying to write a type checker plugin that adds wanted constraint which helps ghc to infer more types. However, it seems that the wanted constraints I add don't get added to the inferred type of the declaration, so that I get a type error like: a.hs:1:1: Warning: Could not deduce (SameLength y x) arising from an application from the context (HLength x ~ HLength y) bound by the inferred type of p :: (HLength x ~ HLength y) => Proxy '(y, x) at a.hs:11:1-69 I think ghc should be able to figure out p :: (SameLength x y, HLength x ~ HLength y) => Proxy '(x,y). The code is self-contained: git clone https://github.com/aavogt/HListPlugin cd HListPlugin/ex make Is this approach supposed to be possible, or am I supposed to rewrite things such that I only produce CtGivenS from the plugin? Regards, Adam

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Injective type families for GHC
by Jan Stolarek 10 Feb '15

10 Feb '15

Haskellers, I am finishing work on adding injective type families to GHC. I know that in the past many people have asked for this feature. If you have use cases for injective type families I would appreciate if you could show them to me. My implementation has some restrictions and I want to see how severe these restrictions are from a practical point of view. Janek --- Politechnika Łódzka Treść tej wiadomości zawiera informacje przeznaczone tylko dla adresata. Jeżeli nie jesteście Państwo jej adresatem, bądź otrzymaliście ją przez pomyłkę prosimy o powiadomienie o tym nadawcy oraz trwałe jej usunięcie.

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GHC 7.10 Prelude: we need your opinion
by Simon Peyton Jones 10 Feb '15

10 Feb '15

Haskell Friends This email asks for your help in deciding how to proceed with some Prelude changes in GHC 7.10. Please read on, but all the info is also at the survey link, here: http://goo.gl/forms/XP1W2JdfpX. Deadline is 21 Feb. The Core Libraries Committee (CLC) is responsible for developing the core libraries that ship with GHC. This is an important but painstaking task, and we owe the CLC a big vote of thanks for taking it on. For over a year the CLC has been working on integrating the Foldable and Traversable classes (shipped in base in GHC 7.8) into the core libraries, and into the Prelude in particular. Detailed planning for GHC 7.10 started in the autumn of 2014, and the CLC went ahead with this integration. Then we had a failure of communication. As these changes affect the Prelude, which is in scope for all users of Haskell, these changes should be held to a higher bar than the regular libraries@ review process. However, the Foldable/Traversable changes were not particularly well signposted. Many people have only recently woken up to them, and some have objected (both in principle and detail). This is an extremely unfortunate situation. On the one hand we are at RC2 for GHC 7.10, so library authors have invested effort in updating their libraries to the new Prelude. On the other, altering the Prelude is in effect altering the language, something we take pretty seriously. We should have had this debate back in 2014, but here we are, and it is unproductive to argue about whose fault it is. We all share responsibility. We need to decide what to do now. A small group of us met by Skype and we've decided to do this: · Push back GHC 7.10's release by at least a month, to late March. This delay also gives us breathing space to address an unrelated show-stopping bug, Trac #9858. · Invite input from the Haskell community on which of two approaches to adopt (this survey<http://goo.gl/forms/XP1W2JdfpX>). The main questions revolve around impact on the Haskell ecosystem (commercial applications, teaching, libraries, etc etc), so we want to ask your opinion rather than guess it. · Ask Simon Marlow and Simon Peyton Jones to decide which approach to follow for GHC 7.10. Wiki pages have been created summarizing these two primary alternatives, including many more points and counter-points and technical details: · Overall summary: https://ghc.haskell.org/trac/ghc/wiki/Prelude710<https://www.google.com/url?q=https%3A%2F%2Fghc.haskell.org%2Ftrac%2Fghc%2Fw…> · Details of Plan List: https://ghc.haskell.org/trac/ghc/wiki/Prelude710/List<https://www.google.com/url?q=https%3A%2F%2Fghc.haskell.org%2Ftrac%2Fghc%2Fw…> · Details of Plan FTP: https://ghc.haskell.org/trac/ghc/wiki/Prelude710/FTP<https://www.google.com/url?q=https%3A%2F%2Fghc.haskell.org%2Ftrac%2Fghc%2Fw…> This survey invites your input on which plan we should follow. Would you please · Read the details of the alternative plans on the three wiki pages above · Add your response to the survey<http://goo.gl/forms/XP1W2JdfpX> Please do read the background. Well-informed responses will help. Thank you! DEADLINE: 21 February 2015 Simon PJ

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Proposal: ValidateMonoLiterals - Initial bikeshed discussion
by Merijn Verstraaten 10 Feb '15

10 Feb '15

I've been repeatedly running into problems with overloaded literals and partial conversion functions, so I wrote up an initial proposal (https://ghc.haskell.org/trac/ghc/wiki/ValidateMonoLiterals) and I'd like to commence with the bikeshedding and hearing other opinions :) Cheers, Merijn

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