wow, this is great work! If theres a clear path to getting the generic tooling into 7.10, i'm all for it :) (and willing to help on concrete mechanical subtasks)
On Wed, Jul 2, 2014 at 12:14 PM, Luite Stegeman <stege...@gmail.com> wrote: > hi all, > > I've added some code [1] [2] to GHCJS to make it run Template Haskell code > on node.js, rather than using the GHC linker. GHCJS has supported TH for a > long time now, but so far always relied on native (host) code for it. This > is the main reason that GHCJS always builds native and JavaScript code for > everything (another is that Cabal Setup.hs scripts need to be compiled to > some host-runnable form, but that can also be JavaScript if you have > node.js) > > Now besides the compiler having to do twice the work, this has some other > disadvantages: > > - Our JavaScript code has the same dependencies (packages) as native code, > which means packages like unix or Win32 show up somewhere, depending on the > host environment. This also limits our options in choosing JS-specific > packages. > - The Template Haskell code runs on the host environment, which might be > slightly different from the target, for example in integer size or > operating system specific constants. > > Moreover, building native code made the GHCJS installation procedure more > tricky, making end users think about libgmp or libiconv locations, since it > basically required the same preparation as building GHC from source. This > change will make installing much easier and more reliable (we still have to > update the build scripts). > > How it works is pretty simple: > > - When any code needs to be run on the target (hscCompileCoreExpr, through > the Hooks API new in GHC 7.8), GHCJS starts a node.js process with the > thrunner.js [3] script, > - GHCJS sends its RTS and the Template Haskell server code [1] to node.js, > the script starts a Haskell thread running the server, > - for every splice, GHCJS compiles it to JavaScript and links it using its > incremental linking functionality. The code for the splice, including > dependencies that have not yet been sent to the runner (for earlier > splices), is then sent in a RunTH [4] message, > - the runner loads and runs the code in the Q monad, can send queries to > GHCJS for reification, > - the runner sends back the result as a serialized Template Haskell AST > (using GHC.Generics for the Binary instances). > > All Template Haskell functionality is supported, including recent > additions for reifying modules and annotations. I still need to clean up > and push the patches for the directory and process packages, but after > that, the TH code can read/write files, run processes and interact with > them and make network connections, all through node.js. > > Now since this approach is in no way specific to JavaScript, I was > wondering if there's any interest in getting this functionality into GHC > 7.10 for general cross compilation. The runner would be a native (target) > program with dynamic libraries (or object files) being sent over to the > target machine (or emulator) for the splices. > > Thanks to Andras Slemmer from Prezi who helped build the initial proof of > concept (without reification) at BudHac. > > cheers, > > Luite > > [1] > https://github.com/ghcjs/ghcjs/blob/414eefb2bb8825b3c4c5cddfec4d79a142bc261a/src/Gen2/TH.hs > [2] > https://github.com/ghcjs/ghcjs-prim/blob/2dffdc2d732b044377037e1d6ebeac2812d4f9a4/GHCJS/Prim/TH/Eval.hs > [3] > https://github.com/ghcjs/ghcjs/blob/414eefb2bb8825b3c4c5cddfec4d79a142bc261a/lib/etc/thrunner.js > [4] > https://github.com/ghcjs/ghcjs-prim/blob/2dffdc2d732b044377037e1d6ebeac2812d4f9a4/GHCJS/Prim/TH/Types.hs#L29 > > _______________________________________________ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > >
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