RE: GHC 7.8 release status

Thank you for the wiki page. This is great. For the first time I have something I can get my teeth into. Some comments · Why aren't you using Data.Dynamic for the hook things? You are precisely doing dynamic typing after all. (Moreover I want to change Data.Dynamic so that it says data Dynamic where Dyn :: Typeable a => a -> Dynamic and you want to take advantage of this. · I don't understand the need for the "key" types and the Hook type to get to the real type. Why not do this: o As now, DynFlags has a map from TypeRep -> Dynamic, with the invariant that if you look up a typerep tr, then the Dynamic you get has typerep tr. o When you want to add a new pass, say for DsForeigns, you say newtype DsForeignsHook = DSF ([LForeignDecl Id ] -> DsM (ForegnStubs, OrdList Binding)) deriving Typeable o To invoke the hook, GHC looks up the type DsForeignsHook in the hook-map, and gets back a newtype value of type DsForeignsHook, which it unwraps and applies. o To install the hook GHC provides a function insertHook : Typeable a => a -> Hooks -> Hooks No need for these strange "data DsForeignsHook = DsForeignsHook" things, or for the Hook type family. Simple! · The design *must* list all the hooks that GHC uses and their types. There's no point in adding a hook that GHC doesn't call! Simon From: Luite Stegeman [mailto:stegeman@gmail.com] Sent: 05 September 2013 02:10 To: Thomas Schilling Cc: Simon Peyton-Jones; Edsko de Vries; ghc-devs Subject: Re: GHC 7.8 release status I've updated the wiki page, expanding the descriptions and adding code from the actual implementation: http://ghc.haskell.org/trac/ghc/wiki/Ghc/Hooks An demo program that uses all hooks here: https://gist.github.com/luite/6444273 (I've listed the users (or proposers) of every hook, and how they use it, Thomas / Edsko, can you check that they indeed do what you need?) The patch is here: https://github.com/ghcjs/ghcjs-build/blob/master/refs/patches/ghc-hooks.patc... In addition to defining the heterogeneous map and the hooks themselves, extra exports have been added to make it possible for users to actually make a hook implementation without copying most of the module's source code. The demo program implements all hooks to check this. Also the GHCJS patch is here: https://github.com/ghcjs/ghcjs-build/blob/master/refs/patches/ghc-ghcjs.patc... It adds the following: - in DynFlags an extra WayCustom constructor to add a custom 'tag' to generated files (GHCJS builds multiple architectures to support Template Haskell among other things, one with the 'js' tag) - in ForeignCall the JavaScriptCallConv calling convention - in Platform an ArchJavaScript architecture - `foreign import javascript' support in the parser and lexer - The JavaScriptFFI extension that enables the `foreign import javascript' syntax, only supported on ArchJavaScript (So using it on a regular GHC would always result in a compile error saying that it's unsupported on the user's platform) luite On Thu, Sep 5, 2013 at 12:17 AM, Thomas Schilling mailto:nominolo@googlemail.com> wrote: I started a wiki page at: http://ghc.haskell.org/trac/ghc/wiki/Ghc/Hooks Luite: could you please fill in the hooks that your latest patch defines? On 4 Sep 2013, at 19:40, Simon Peyton-Jones mailto:simonpj@microsoft.com> wrote:

I do need more than a patch, please, please. A wiki page explaining the design, as seen by the user (of the GHC API), the problems it solves, and the use-cases it enables, would be most helpful.

Simon

| -----Original Message----- | From: Thomas Schilling [mailto:nominolo@googlemail.commailto:nominolo@googlemail.com] | Sent: 04 September 2013 17:26 | To: Simon Peyton-Jones; Luite Stegeman | Cc: Nicolas Frisby; "Pedro Magalhães (dreixel@gmail.commailto:dreixel@gmail.com)"; Richard | Eisenberg (eir@cis.upenn.edumailto:eir@cis.upenn.edu); Geoffrey Mainland | (mainland@cs.drexel.edumailto:mainland@cs.drexel.edu); Iavor Diatchki; Austin Seipp; Edsko de Vries; | Ryan Newton (rrnewton@gmail.commailto:rrnewton@gmail.com); David Luposchainsky; ghc- | devs@haskell.orgmailto:devs@haskell.org | Subject: Re: GHC 7.8 release status | | | On 4 Sep 2013, at 15:52, Simon Peyton-Jones mailto:simonpj@microsoft.com> | wrote: | | > Edsko/Thomas/Luite: if you want anything for 7.8 it'll have to be | jolly soon. At the moment I don't even know the motivation or design, | let alone implementation. Could you make a wiki page explaining the | proposed design? Is it really important to do this for 7.8? | | Yes, it is quite important to get this into 7.8. Not having these | features in GHC makes it very difficult for people to adopt GHCJS. One | could argue that GHCJS is not yet production-ready anyway and users that | want to try it can figure out building GHC from source to use it, but | this doesn't quite apply. | | 1. GHCJS targets a wider audience than users brave enough to compile | GHC from source. In addition, the next chance to get these features into | GHC is in a year from now, so when GHCJS becomes more mature then this | will be a major hurdle for adoption. | | 2. These changes are also required for IDE tools which really mustn't | require users to build a custom version of GHC. | | | Luite's design is actually very flexible. It simply allows GHC API | users to provide functions that are called instead of (or in addition | to) existing functions in GHC. Instead of calling, say, "genHardCode", | the driver now looks up whether the user has specified a hook for | genHardCode and calls that instead. | | Currently we only specify a small number of hooks that are sufficient | for our use cases. Future releases of GHC can be extended to include | more hooks, if that is needed. | | Hooks are stored as an untyped map inside the DynFlags (to avoid issues | with circular dependencies). Each hook is looked up using a single- | constructor type and type families are used to make this type safe. | There is one use of unsafeCoerce to avoid having to make every hook | function an instance of Typeable. | | Unlike CorePlugins, it is only a GHC API feature, and users cannot | specify plugins to be added via command line options. If we can come up | with a good design, then we could add this in GHC 7.10, but it is not | necessary at this point. | | Luite: Do you have a link to your latest patch?