- ghc-devs - Haskell.org

Conveniently searching GitLab
by Ben Gamari 06 Aug '19

06 Aug '19

Hello everyone, I've long found GitLab's search interface to be rather clunky. Several of the issues I've noted have been reported upstream but progress in resolving them seems to be slow. Consequently, I have implemented a workaround [1] which addresses most of my typical use-cases. This is essentially a thin wrapper around GitLab's various search facilities which intelligently routes requests according to a simple (and hopefully intuitive) query syntax. For instance, to * navigate to GHC issue #123: search for `#123` * search for GHC issues related to unboxed tuples: search for `# unboxed tuples` * navigate to the `ghc/head.hackage` project: search for `ghc/head.hackage>` * navigate to merge request !3 of the `ghc/head.hackage` project: search for `ghc/head.hackage!3` * navigate to commit e130fb57f7991575d848612abafe9ad10129131c of the `ghc/ghc` project: search for `ghc/ghc@e130fb57f7991575d848612abafe9ad10129131c` * search for merge requests of `haskell/ghcup` pertaining to Darwin: search for `haskell/ghcup! Darwin` Note that, as seen in the first two examples, the project name defaults to `ghc/ghc` if omitted. This interface is best used via your browser's search keywords feature [2]. To add a search keyword in Firefox you can right click on the search query input field and select "Add search keyword". To my surprise I didn't find a similarly convenient shortcut in Chromium. If you can think of any way in which the service can be improved, feel free to open a pull request against the upstream repository [3]. Cheers, - Ben [1] https://search.gitlab.haskell.org/ [2] http://kb.mozillazine.org/Using_keyword_searches [3] https://gitlab.haskell.org/bgamari/gitlab-search-service

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Solving stuck type families with a TC plugin
by Sandy Maguire 05 Aug '19

05 Aug '19

Hi all, I'm attempting to use a plugin to solve a generic type family CmpType (a :: k) (b :: k) :: Ordering by doing some sort of arbitrary hashing on `a` and `b` and ensuring they're the same. In the past, I've been successful at getting GHC to unify things by emitting new wanted CNonCanonical cts. This sort of works: mkWanted :: TyCon -> CompareType -> TcPluginM Ct mkWanted cmpType cmp = do (ev, _) <- unsafeTcPluginTcM . runTcSDeriveds $ newWantedEq (cmpTypeLoc cmp) Nominal (cmpTypeType cmp) (doCompare cmp) pure $ CNonCanonical ev Which is to say that this will compile: foo :: Proxy 'EQ foo = Proxy @(CmpType 2 2) So far so good! However, this acts strangely. For example, if I ask for bar with the incorrect type: bar :: Proxy 'GT bar = Proxy @(CmpType 2 2) I get the error: • Couldn't match type ‘CmpType 2 2’ with ‘'GT’ Expected type: Proxy 'GT Actual type: Proxy (CmpType 2 2) when I would expect • Couldn't match type ‘'EQ’ with ‘'GT’ This is more than just an issue with the error messages. A type family that is stuck on the result of CmpType, even after I've solved CmpType via the above! type family IsEQ (a :: Ordering) :: Bool where IsEQ 'EQ = 'True IsEQ _ = 'False zop :: Proxy 'True zop = Proxy @(IsEQ (CmpType 2 2)) • Couldn't match type ‘IsEQ (CmpType 2 2)’ with ‘'True’ Expected type: Proxy 'True Actual type: Proxy (IsEQ (CmpType 2 2)) Any suggestions for what I might be doing wrong, and how to convince GHC to make `zop` work properly? Thanks!

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a better workflow?
by Richard Eisenberg 04 Aug '19

04 Aug '19

Hi devs, Having gotten back to spending more time on GHC, I've found myself frequently hitting capacity limits on my machine. At one point, I could use a server at work that was a workhorse, but that's not possible any more (for boring reasons). It was great, and I miss it. So I started wondering about renting an AWS instance to help, but I quickly got overwhelmed by choice in setting that up. It's now pretty clear that their free services won't serve me, even as a trial prototype. So before diving deeper, I thought I'd ask: has anyone tried this? Or does anyone have a workflow that they like? Problems I have in want of a solution: - Someone submits an MR and I'm reviewing it. I want to interact with it. This invariably means building from scratch and waiting 45 minutes. - I work on a patch for a few weeks, on and off. It's ready, but I want to rebase. So I build from scratch and wait 45 minutes. - I make a controversial change and want to smoke out any programs that fail. So I run the testsuite and wait over an hour. This gets tiresome quickly. Most days of GHC hacking require at least one forced task-switch due to these wait times. If I had a snappy server, perhaps these times would be lessened. By the way, I'm aware of ghc-artefact-nix, but I don't know how to use it. I tried it twice. The first time, I think it worked. But by the second time, it had been revamped (ghc-head-from), and I think I needed to go into two subshells to get it working... and then the ghc I had didn't include the MR code. I think. It's hard to be sure when you're not sure whether or not the patch itself is working. Part of the problem is that I don't use Nix and mostly don't know what I'm doing when I follow the ghc-artefact-nix instructions, which seem to target Nix users. Thanks! Richard

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Invalid link in the wiki page "Building GHC on Windows"
by Joan Karadimov 04 Aug '19

04 Aug '19

Inside this wiki page: https://gitlab.haskell.org/ghc/ghc/wikis/building/preparation/windows ... there is a link to the latest cabal release. The link is: https://www.haskell.org/cabal/release/cabal-install-2.4.1.0/cabal-install-2… That link is not valid. It should be something like: https://downloads.haskell.org/cabal/cabal-install-2.4.1.0/cabal-install-2.4… The latter link is taken from https://www.haskell.org/cabal/download.html.

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api to access .hi files
by Sam Halliday 02 Aug '19

02 Aug '19

Hello all, I'd like to learn how to use the ghc api programmatically, but I am finding the haddocks (on hackage) to be a bit overwhelming. Could somebody please help me out by pointing me in the direction of the parts of the haddocks that are relevant to access information from .hi files that are available in the current build environment? In particular, I'm mostly interested in gathering information about symbols and their type signatures. As a first exercise: given a module+import section for a haskell source file, I want to find out which symbols (and their types) are available. Like :browse in ghci, but programmatically. PS: I'm aware that the .hie format is up and coming. I'm very excited by this! But I'm going to be using ghc-8.4.x and ghc-8.6.x for the foreseeable future, so I am mostly interested in what they have to offer. -- Best regards, Sam

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GitLab upgraded
by Ben Gamari 01 Aug '19

01 Aug '19

Hi everyone, Yesterday I upgraded GitLab to 12.1 and added a few patches specific to the GHC instance. There are a few effects: 1. issue and merge request numbers are now the first thing displayed in the page title of merge request and issue pages. 2. issue and merge request numbers are also shown at the beginning of email subject lines. 3. due to an apparent regression, GitLab's CI configuration validator started rejecting our .gitlab-ci.yml. I have fixed this in 5e04841c4641e2249066614065053166657e3eb4. If you see mysterious "yaml invalid" errors in your CI results you should try rebasing on to current `master`. Cheers, - Ben

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Extended Dependency Generation Proposal
by David Eichmann 30 Jul '19

30 Jul '19

Hello GHC Developers, I've recently been working on a proposal (found here <https://github.com/ghc-proposals/ghc-proposals/pull/245>[1]) for "Extended Dependency Generation". This new feature takes the form of a new build option/mode that outputs comprehensive build dependencies for building Haskell modules. This allows external build tools, such as cabal-install, to implement correct incremental builds with recompilation avoidance using GHC's one shot mode to compile individual modules. All input is appreciated. It would be particularly helpful to hear from the Cabal, Stack, and Shake communities. Looking forward to hearing your comments, David Eichmann [1] https://github.com/ghc-proposals/ghc-proposals/pull/245 -- David Eichmann, Haskell Consultant Well-Typed LLP, http://www.well-typed.com Registered in England & Wales, OC335890 118 Wymering Mansions, Wymering Road, London W9 2NF, England

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Most recent happy and Alex releases can’t build ghc 8.6.x
by Carter Schonwald 27 Jul '19

27 Jul '19

Hey everyone : Is this a known issue / deliberate breaking change / other ? This is also the same Alex and happy that’s needed to build current ghc master Thx! -Carter

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can't checkout ghc 8.6 branch correctly -- something wrong with transformers mirror repo?
by Carter Schonwald 26 Jul '19

26 Jul '19

Hey everyone, whats wrong with the 8.6 branch? when i do a fresh clone, i wind up with this error : $ git submodule update --init --recursive error: Server does not allow request for unadvertised object def8c55d0c47c1c40de985d83f052f3659b40cfd Fetched in submodule path 'libraries/transformers', but it did not contain def8c55d0c47c1c40de985d83f052f3659b40cfd. Direct fetching of that commit failed. 14:17:43 ~/D/r/ghc-8.6.5-series (ghc-8.6|✚6) $

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Try haskell-ide-engine on GHC!
by Matthew Pickering 26 Jul '19

26 Jul '19

Hi all, As some of you know I have been working on getting haskell-ide-engine working on GHC for the last few months. Perhaps now the branch is in a usable state where people can try it and report issues. All the basic features such as, hover, completion, error reporting, go to definition etc should work well. I suspect this will be enough for most developers. I have compiled a list of instructions about how to try out the branch. https://gist.github.com/mpickering/68ae458d2c426a29a7c1ddf798dbc793 In the last few weeks Zubin has been a great help finishing some parts of the patch that I lost steam for and given it a much better chance of getting merged into the main repo before the end of the year. Cheers, Matt

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