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Question about TypeInType
by Iavor Diatchki 16 Apr '18

16 Apr '18

Hello, I was experimenting with TypeInType and run into a problem, that can be reduced to the following example. Does anyone have any insight on what causes the error, in particular why is `IxKind` not being reduced? -Iavor {-# Language TypeInType, TypeFamilies #-} module Help where import Data.Kind type family IxKind (m :: Type) :: Type type family Value (m :: Type) :: IxKind m -> Type data T (k :: Type) (f :: k -> Type) type instance IxKind (T k f) = k type instance Value (T k f) = f {- [1 of 1] Compiling Help ( Desktop/Help.hs, interpreted ) Desktop/Help.hs:13:31: error: • Expected kind ‘IxKind (T k f) -> *’, but ‘f’ has kind ‘k -> *’ • In the type ‘f’ In the type instance declaration for ‘Value’ | 13 | type instance Value (T k f) = f | ^ Failed, no modules loaded. -}

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RE: Nested Implications
by Simon Peyton Jones 16 Apr '18

16 Apr '18

Mathias I suspect substImplication was removed simply because it was never called, but I’m not certain. The entire cloning and substitution business is very heavyweight. Here’s an alternative idea: * Gather ‘fuvs’, the set of all free unification variables of the constraint you are about to solve. * Solve the constraint * For each variable in ‘fuvs’, set its IORef to Flexi; that is, simply undo any unification that has taken place. That seems simple, very non-invasive, and robust. Simon From: Matthías Páll Gissurarson <pallm(a)student.chalmers.se> Sent: 10 April 2018 00:57 To: Simon Peyton Jones <simonpj(a)microsoft.com> Subject: Nested Implications Greetings Simon, I've been working on implementing the valid substitutions for typed holes in terms of nested implications, and I think I've worked out how to do it. But one thing bothers me. To use the implications that are passed along with the ReportErrCtxt, I have to clone the type variables within, to avoid having side-effects that could impact later searches. I clone the type variables and create a substitution from the old variables to the new, which I'd like to apply to the implication. When I was looking around for how to do that, I came across this code in GHC 7.6.3 https://downloads.haskell.org/~ghc/7.6-latest/docs/html/libraries/ghc-7.6.3…<https://na01.safelinks.protection.outlook.com/?url=https:%2F%2Fdownloads.ha…> The `substImplication` function does precisely what I want, i.e. applies a substitution to an implication. However, that code is no longer present in GHC 8.5! The git history doesn't go far enough back for me to find an explanation, so I wanted to ask: why was this function removed? Is there something I should be wary of if I re-implement it? Please correct me if my approach is all wrong, I'd like to hear what you had in mind. -- - Matthías Páll Gissurarson

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GHC Core / STG to supercombinators
by Csaba Hruska 16 Apr '18

16 Apr '18

Hello, I'd like to use GHC as a haskell frontend in a project. I wonder what is the easiest way to compile Haskell to supercombinators (top level functions) using GHC as a library. Is it possible to use the simplifier to transform the parsed Haskell source to supercombinators? i.e. to do - eta expansion - closure conversion - lambda lifting Regarding the eta expansion and lambda lifting it seems (according the comments in simplifier code) it does not guarantee to make these transformations in every case. If GHC could transform the Core representation to supercombinators, which transformation should I use from *CoreToDo*? https://github.com/ghc/ghc/blob/master/compiler/simplCore/CoreMonad.hs#L107- L135 I'd like to use GHC as a frontend for my custom code generator which can handle (lazy) top level functions only. Is it better to use GHC as a library or is it better to write a compiler plugin to capture the core representation. I do not want to optimize the Core at all neither want to use other parts of GHC's backend (i.e. codegen). Ideally GHC would typecheck and transform everything to top level function and my system would do the rest. Do you know what would be the easiest way to do this? (i.e. via *CoreToDo* or custom calls for the simplifying functions) Or would it be simpler to generate top level (lazy) functions from STG? Regards, Csaba Hruska

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Site of ghc.haskell.org is down?
by Takenobu Tani 16 Apr '18

16 Apr '18

Hi devs, When I accessed `https://ghc.haskell.org/`, the following message is displayed: Your connection is not secure I checked it with Firefox and Chrome. Is it a matter of site setting? Regards, Takenobu

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Error submitting a code review
by ARJANEN Loïc Jean David 13 Apr '18

13 Apr '18

Hello, I'm currently having an issue submitting my first code review. I recently registered on Phabricator and tried to send my first code review through the web interface. However, Harbormaster is failing to build it with the following error in the lease: Couldn't find remote ref. When searching on Google for this error, I found indications that it's related to Drydock not managing to push the changes to the staging area, likely due to a bad SSH key or git URL for arcanist. Could the SSH key issue also apply when using the web interface?Hoping to read from you soon, I wish you a very good day. Yours sincerely,ARJANEN Loïc

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DTrace patch for FreeBSD breaks ability to function as a bootstrap compiler under FreeBSD
by raichoo 13 Apr '18

13 Apr '18

Hi, Last year I've provided a patch that enables DTrace probes under FreeBSD, sadly as it turns out this currently breaks the ability of GHC 8.4.1 to function as a bootstrap compiler under FreeBSD. I've provided a patch that adds a flag to the build system so one can turn off DTrace in case one needs to build a bootstrap compiler. https://phabricator.haskell.org/D4575 This should probably also contain some heads up in the documentation, otherwise someone might end up with a compiler that's not suitable for bootstrapping. Not sure on how this is being handled. I have an idea on how to fix the actual issue but for the time being this might be a suitable workaround. Maybe we can still get this into 8.4.2? I've already notified the FreeBSD ports maintainers regarding this issue. Sorry for the inconvenience. Kind regards, raichoo

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Re: [ANNOUNCE] GHC 8.4.1 released
by Ryan Scott 12 Apr '18

12 Apr '18

I've submitted a Diff [1] for this. Ryan S. ----- [1] https://phabricator.haskell.org/D4586

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Re: [ANNOUNCE] GHC 8.4.1 released
by Ryan Scott 11 Apr '18

11 Apr '18

Thanks, Ben. It looks like the version number for base has not been bumped to 4.11.1.0, despite incorporating this commit [1] which introduces readFieldHash to base. Currently, this makes it impossible to guard against the existence of the readFieldHash function in a project I'm working on. Ryan S. ----- [1] http://git.haskell.org/ghc.git/commit/d5577f44eaf3b9dfdfc77828038782bf818c1…

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TcPluginContradiction understanding problem and converting Type to Typeable
by alice 11 Apr '18

11 Apr '18

Hello, I'm writing a type-checker plugin for ghc, and I'm stuck on two problems. I can't understand how does TcPluginContradiction work. My problem is, when I do TcPluginContradiction listOfFailedConstraints and run the plugin on something which should fail, compiler output contains strange errors for places which doesn't produce any errors when the rest type checks. And it can be seen from debug that listOfFailedConstraints does contain only the constraints that are expected to fail. For example my plugin should type check Set '[Int]) ~ Set '[Int, Int], and should not Set '[Int, Bool, Int] ~ Set '[Int]. And everything is great when I run it on the first case, but if I run it on the both first and second, the compiler output will contain «Couldn't match type ‘Set '[Int]’ with ‘Set '[Int, Int]’» and «Couldn't match type ‘Set '[Int, Bool, Int]’ with ‘Set '[Int]’». My ghc version is 8.2.2. Also how does ghc converts Type from https://hackage.haskell.org/package/ghc-8.2.1/docs/src/TyCoRep.html#Type <https://hackage.haskell.org/package/ghc-8.2.1/docs/src/TyCoRep.html#Type> to Typeable/TypeRep from https://hackage.haskell.org/package/base-4.10.1.0/docs/src/Data.Typeable.In… <https://hackage.haskell.org/package/base-4.10.1.0/docs/src/Data.Typeable.In…>? I’d like to use a function (if there exists one) that takes Type and returns its fingerprint (https://hackage.haskell.org/package/base-4.10.1.0/docs/src/GHC.Fingerprint.… <https://hackage.haskell.org/package/base-4.10.1.0/docs/src/GHC.Fingerprint.…>). Thank you for your time, Alice.

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ghc-8.4.1-release tag
by Joachim Breitner 10 Apr '18

10 Apr '18

Hi, I noticed that the tag ghc-8.4.1-release points to f31c40efdc918bc9da8a325327ba5a472bd6ea9e but the tarball has different content: $ cat /tmp/ghc-8.4.1/GIT_COMMIT_ID 0a3e2f324dbd525d626ebd3d97e8ffa1cf2f0ffb Ben, would you mind updating the git tag to reflect reality, to avoid confusion (it’s be a forced tag update, but still better than inconsistent information). Cheers, Joachim -- Joachim “nomeata” Breitner mail(a)joachim-breitner.de https://www.joachim-breitner.de/

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