June 2014 - ghc-devs - Haskell.org

Case expressions in STG
by Tom Ellis 21 Jun '14

21 Jun '14

I am reading SPJ's seminal work "Implementing lazy functional languages on stock hardware: the Spinless Tagless G-machine" (1992). The paper is available here http://citeseer.ist.psu.edu/viewdoc/summary?doi=10.1.1.53.3729 On p62 we see "The expression scrutinised by a case expression must eventually evaluate either to a primitive value or a constructor application.". This doesn't make sense to me. Isn't the following a valid STG program? What am I missing? Where is it specified that the scrutinee of a case expression cannot be of a function type? {x} \n {z} -> let f = \{x} \n {y} -> g x y in case f of f' -> f' z Thanks, Tom

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Uniquable RdrName instance
by Jan Stolarek 20 Jun '14

20 Jun '14

Hi all, I just found myself in the need of Uniquable instance for RdrName. I'm surprised that such instance does not exist already because other datatypes like Name or OccName already have Uniquable instances. So, is there a reason why Uniquable instance for RdrName does not exist already (other than "it wasn't needed")? How should such an instance look like? I made an attempt: rdrNameUnique :: RdrName -> Unique rdrNameUnique (Unqual occName) = getUnique occName rdrNameUnique (Qual _ occName) = getUnique occName rdrNameUnique (Orig _ occName) = getUnique occName rdrNameUnique (Exact name ) = getUnique name But I suspect this might be wrong: - cases 1 and 4 simply return a Unique for the OccName/Name stored inside RdrName. I think this will assign the same Unique to RdrName and corresponding OccName/Name. Is this allowed? - cases 2 and 3 ignore the Module stored inside RdrName. Again, this assigns the RdrName with a Unique identical to OccNames stored inside it. Help appreciated. Janek

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Proposal: Partial Type Signatures
by Thomas Winant 19 Jun '14

19 Jun '14

Dear GHC developers, Together with Tom Schrijvers, Frank Piessens and Dominique Devriese, I have been working on a proposal for adding *Partial Type Signatures* to GHC. In a partial type signature, annotated types can be mixed with inferred types. A type signature is written like before, but can now contain wildcards, written as underscores. The types of these wildcards or unknown types will be inferred by the type checker, e.g. foo :: _ -> Bool foo x = not x -- Inferred: Bool -> Boo The proposal also includes a form of generalisation which aligns with the existing generalisation that GHC does. We have written down a motivation (when and how might you use this) and details about the design and implementation on the following wiki page: https://ghc.haskell.org/trac/ghc/wiki/PartialTypeSignatures We have a (work in progress) implementation [1] of the feature based on GHC. It currently implements most of what we propose, but there are some remaining important bugs mostly concerning the generalisation. We also described our design and presented a formalisation based on the OutsideIn(X) formalism in a paper [2] presented at PADL'14. What we are hoping to get from the people on this list is any of the below: * Read the design, play with the implementation and tell us any comments you may have about the feature, its design and implementation. * Opinions on whether this feature might be acceptable in GHC upstream at some point (if not, we do not think it's worth developing the implementation much further). * Perhaps a code review or a discussion with someone more knowledgeable about the internals of GHC's type checker about how we might fix the remaining problems in our implementation (specifically, we could use some help with implementing the generalisation of partial type signatures). * Feedback on the `Questions and issues' section on the wiki page. Kind regards, Thomas Winant [1]: https://github.com/mrBliss/ghc-head/ [2]: https://lirias.kuleuven.be/bitstream/123456789/423475/3/paper.pdf Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm

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GHC MinGW distribution
by Robin KAY 18 Jun '14

18 Jun '14

Dear All, I wanted to enquire about the prospects for updating the version of MinGW which ships with the Windows binary distribution of GHC. The version included as of 7.8.2 is now several years old and in some cases I've found that it's incompatible with the libraries produced by newer versions of MinGW (as to be expected, per my understanding). Specifically, my HsQML binding for Qt can't be used with the libraries from the official Windows binary distribution of Qt 5 because the resulting executables crash on start-up with runtime incompatibilities. I'm in the process of trying to build out-of-the-box compatible Qt binaries against GHC's MinGW, but Qt's stated minimum requirements on the tool-chain version aren't encouraging. The only way I currently have of making this work is for users to edit their GHC settings file to point GHC at a version of gcc.exe from a newer MinGW (such as the one which ships with Qt). The fact that this seems to work is encouraging, but it's still a bit of a difficult process to put people through. I know that Windows developers are in short supply, so I would like to offer what assistance I can in making this happen. There appear to be copies of MinGW stored in the GHC repository at http://git.haskell.org/ghc-tarballs.git/tree . Does the build system use these automatically or are they just there for reference? Thanks, -- Robin KAY

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Offering GHC builder build slaves
by Alain O'Dea 18 Jun '14

18 Jun '14

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi folks: I have successfully built Ian Lynagh's GHC builder on Ubuntu and SmartOS and I would like to offer build slaves based on Carter's mirroring of the code to https://github.com/cartazio/ghc-builder. I can offer several build slaves, but I'm not sure what the process is. How do I run multiple build slaves? Do I need a separate username for each? Is there a username convention? The suggestion at https://ghc.haskell.org/trac/ghc/wiki/Builder is that I post a username and password to ghc@. There are two issues with this: 1. ghc@ does not exist as far as I can tell 2. Posting a password to a mailing list will make it publicly accessible and allow others to impersonate my build slaves I am happy to send this information if the admins of the GHC builder infrastructure are comfortable with the risks. Alternatively, I am able to send this via GPG encrypted email given the public key and email of an admin. Feel free to contact me on or off list about this. Best, Alain -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.14 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJTQ0uTAAoJEP0rIXJNjNSA+fMH/2p9yeWgpfDeaTHilur5qoZ6 6DZiktJgvMpVeqFwHyaFMk+ubEp8/xU/VUrOEztr01jmzNLS2UoqDVH/7EZPZPtV 0ONh/bcYYA8EBa9SCqaVXVb9I8EdDE6w2cQGDqnwHqaFerAUqv8OiQEWyJCuJSdr 7EL/vcacNfr5Ix4oG2pkESvEJBHHEN4ZTXoKeJnyQT93o2RaC1fgImm6F6tgpdQE Jh+QInIX1dRuSl+pDlHg6kbLZqFG8Mnyz0bcWuUL2ekGQBp3HtT0MwonM9HUTmmG 0baRYUaK/moO5Q6lUXhI2eRT/UFl4qnzwJw/sIVuaL7h1Ikj0ZMOuPs0GjfRbY8= =/Rwk -----END PGP SIGNATURE-----

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Deep embeddings and Arrows Re: Uniquable RdrName instance
by Carter Schonwald 17 Jun '14

17 Jun '14

to clarify: having bind would be equivalent to having arr for the purposes of my question (assuming its the standard monadic bind). having arr :: (b -> c) -> a b c is tantamount to assuming that any haskell function can be embedded in an arrow instance which prevents a lot of interesting deep embedding uses of the Arrow abstraction/ or at least makes it a bit tricker. (eg things like writing circuits or certain types of compiled FRP models). On Tue, Jun 17, 2014 at 4:06 AM, Jan Stolarek <jan.stolarek(a)p.lodz.pl> wrote: > > FYI it's #7828, not #7282. > Of course, yes. > > > would making arrow remindable involve dropping the arr == haksell > functions assumption or doing > > something that would allow generalized arrows? > Not sure if I fully understand what you mean. There's an idea to give up > on current desugaring > that heavily uses arr, >>> etc. in favor of desugaring based on bind > equivalents for arrows. Is > this what you wanted to know? There's some discussion on the Trac you > might want to follow. > > Janek > _______________________________________________ > ghc-devs mailing list > ghc-devs(a)haskell.org > http://www.haskell.org/mailman/listinfo/ghc-devs >

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RE: Regression in the typechecker in GHC 7.8.2
by Simon Peyton Jones 16 Jun '14

16 Jun '14

Copying ghc-devs. Oleg says: | Sorry for reporting a problem via e-mail. It seems track no | longer accepts anonymous (guest) submissions. When I tried to register | the account I was told that my submission is a spam. The tracker is | really well protected. Can anyone help him? I'll open a ticket. Simon | -----Original Message----- | From: oleg(a)okmij.org [mailto:oleg@okmij.org] | Sent: 16 June 2014 11:46 | To: Simon Peyton Jones | Subject: Regression in the typechecker in GHC 7.8.2 | | | Hello! | | Sorry for reporting a problem via e-mail. It seems track no | longer accepts anonymous (guest) submissions. When I tried to register | the account I was told that my submission is a spam. The tracker is | really well protected. | | Here is the problem: what used to type check in GHC 7.4.1 (and I think | in 7.6.2, although I no longer have access to that version) fails in GHC | 7.8.2. | | The following program type-checks with GHC 7.4.1 and GHC 7.8.2: | | {-# LANGUAGE RankNTypes #-} | {-# LANGUAGE TypeFamilies #-} | | module T where | | foo :: (forall f g. (Functor f) => f a -> f b) -> [a] -> [b] | -- foo :: (forall f g. (Functor f, g ~ f) => g a -> g b) -> [a] -> [b] | foo tr x = tr x | | t = foo (fmap not) [True] | | The following code (which differs only in the signature of foo) | | {-# LANGUAGE RankNTypes #-} | {-# LANGUAGE TypeFamilies #-} | | module T where | | -- foo :: (forall f g. (Functor f) => f a -> f b) -> [a] -> [b] foo :: | (forall f g. (Functor f, g ~ f) => g a -> g b) -> [a] -> [b] foo tr x = | tr x | | t = foo (fmap not) [True] | | | type-checks with 7.4.1 but not with 7.8.2. The latter reports the error | | Couldn't match type `b' with `Bool' | `b' is untouchable | inside the constraints (Functor f, g ~ f) | bound by a type expected by the context: | (Functor f, g ~ f) => g Bool -> g b | at /tmp/t.hs:12:5-25 | `b' is a rigid type variable bound by | the inferred type of t :: [b] at /tmp/t.hs:12:1 | Expected type: Bool -> b | Actual type: Bool -> Bool | Relevant bindings include t :: [b] (bound at /tmp/t.hs:12:1) | In the first argument of `fmap', namely `not' | In the first argument of `foo', namely `(fmap not)' | | Giving t the type signature [Bool] fixes the problem. Alas, I come | across the similar untouchable error in situations where giving the type | signature is quite difficult (in local bindings, with quite large | types). | | Sorry again for the off-line report, | Oleg

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Getting error about unused instances during "sh validate"
by Alfredo Di Napoli 13 Jun '14

13 Jun '14

Hello guys, am I the only one to get the following when I run "sh validate"? libraries/base/Data/Maybe.hs:139:1: Warning: Defined but not used: ‘mapMaybeFB’ <no location info>: Failing due to -Werror. make[1]: *** [libraries/base/dist-install/doc/html/base/base.haddock] Error 1 make[1]: *** Waiting for unfinished jobs.... make: *** [all] Error 2 I'm working on this ticket, but I can't see how that can be related: https://ghc.haskell.org/trac/ghc/ticket/8226 Thanks! Alfredo

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HEADS-UP: diagrams does not compile with HEAD (regressions)
by Gabor Greif 12 Jun '14

12 Jun '14

Devs, as of recently GHC HEAD stopped building the diagrams library. Several prerequisite libs also fail to compile. A specific error message appears in an attoparsec issue <https://github.com/bos/attoparsec/issues/67>, for which I have submitted a workaround. But as Herbert cautiously points out, this could be a recent GHC bug surfacing. The symptoms of the bug seem to be that GHC complains about the usage of (~) type equality operation, but there is no reference to that type operator in the source code. To work around the problem it suffices to add -XGADTs or -XTypeFamilies. Does this ring any bells? Can automatized tests catch such things in the future? Cheers, Gabor

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Re: GHC/cabal release procedures, and Stackage
by Joachim Breitner 11 Jun '14

11 Jun '14

Hi Michael, Am Samstag, den 07.06.2014, 21:06 +0300 schrieb Michael Snoyman: > If there was a daily snapshot build, I would be happy to set up some > kind of regular process to download that snapshot and do a Stackage > run on it. I'm currently blocked on this kind of activity, since I > can't get a successful GHC 7.8 build due to my system using the Gold > linker. That would be great, both for GHC and for people who want to have their packages work on GHC HEAD without manually monitoring it. There is http://deb.haskell.org/ which should produce daily debian packages for Debian wheezy. I guess if you are building on that platform, such packages are easiest to use (as you need no particular tooling to update and install). http://deb.haskell.org/dailies/latest/ is currently lagging due to temporary full disk, but I hope that by tomorrow, we have a new build. There used to be daily snapshot builds at http://darcs.haskell.org/ghcBuilder/uploads/ but that is defuct (Can someone remove the link from http://www.haskell.org/ghc/download) I wonder if the “new” builder infrastructure at http://haskell.inf.elte.hu/builders/ assembles the snapshots somewhere, then you can use them. Or you can build GHC yourself as part of the stackage run. Greetings, Joachim -- Joachim “nomeata” Breitner mail(a)joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata(a)joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata(a)debian.org

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