- Glasgow-haskell-users

How to get started with a new backend?
by Jason Dagit 29 Jan '13

29 Jan '13

I would like to explore making a backend for .NET. I've done a lot of background reading about previous .NET and JVM attempts for Haskell. It seems like several folks have made significant progress in the past and, with the exception of UHC, I can't find any code around the internet from the previous efforts. I realize that in total it's a huge undertaking and codegen is only one of several significant hurdles to success. I would like to get a very, very, very simple translation working inside GHC. If all I can compile and run is fibonacci, then I would be quite happy. For my first attempt, proof of concept is sufficient. I found a lot of good documentation on the ghc trac for how the compilation phases work and what happens in the different parts of the backend. The documentation is excellent, especially compared to other compilers I've looked at. When I started looking at how to write the code, I started to wonder about the "least effort" path to getting something (anything?) working. Here are some questions: * Haskell.NET seems to be dead. Does anyone know where their code went? * Did lambdavm also disappear? (JVM I know, but close enough to be useful) * Would it make sense to copy&modify the -fvia-C backend to generate C#? The trac claims that ghc can compile itself to C so that only standard gnu C tools are needed to build an unregistered compiler. Could I use this trick to translate programs to C#? * What stage in the pipeline should I translate from? Core? STG? Cmm? * Which directories/source files should I look at to get familiar with the code gen? I've heard the LLVM codegen is relatively simple. * Any other advice? Thank you in advance! Jason

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Fastest way to reload module with GHC API
by JP Moresmau 28 Jan '13

28 Jan '13

Hello, I just want to be sure of what's the fastest way to reload a module with the GHC API. I have a file whose path is fp I load the module with: addTarget Target { targetId = TargetFile fp Nothing, targetAllowObjCode = True, targetContents = Nothing } Then I load the module load LoadAllTargets And when I want to reload the module (the contents of fp have changed) I do: removeTarget (TargetFile fp Nothing) load LoadAllTargets and then I rerun my initial code (addTarget, load) This works well, I don't get any errors about duplicates, the information I extract from the module is updated properly. But is it the most efficient, or can I achieve the same thing faster (I'm looking at improving the performance of my BuildWrapper code and by consequence of EclipseFP)? Thanks! -- JP Moresmau http://jpmoresmau.blogspot.com/

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Size of crosscompiled exectuable
by Nathan Hüsken 28 Jan '13

28 Jan '13

Hey, A simple hello world application has 1Mb in by 64 bit ubunut machine. When I stript it, is has about 750kb. When I build a cross compiler for android (arm), the executable has a asize of about 10MB, stripped about 5MB. That is huge, five times the size on my linux sysem. Why is this? Can I do something about it? Thanks! Nathan

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Request for review of a GADT tutorial draft
by Anton Dergunov 28 Jan '13

28 Jan '13

Dear Haskell community, I have recently written an introductory-level tutorial article about GADTs in GHC (inspired by LASER 2012 summer school and to be submitted to their proceedings). I have already send this draft to the "Haskell Cafe" mailing list, but I was also advised to use these mailing lists, so I would like to ask for your feedback: http://anton-dergunov.ru/publications/gadts_draft_v4.pdf Any opinion about this article and any suggestions are very welcome! -- Best Regards, Anton Dergunov

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data kinds
by Ross Paterson 27 Jan '13

27 Jan '13

GHC implements data kinds by promoting data declarations of a certain restricted form, but I wonder if it would be better to have a special syntax for kind definitions, say data kind Nat = Zero | Succ Nat At the moment, things get promoted whether you need them or not, and if you've made some mistake that makes your definition non-promotable you don't find out until you try to use it. More importantly, a separate form for kinds would allow one to use existing kinds, i.e. *, in definitions of new kinds.

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Re: Error building ghc on raspberry pi.
by roconnor＠theorem.ca 27 Jan '13

27 Jan '13

On Thu, 3 Jan 2013, Thijs Alkemade wrote: > I believe I had the same problem, which disappeared after upgrading llvm from 3.0 to 3.1, and using that instead for ./configure. > > Hope this helps, > Thijs Thanks, using LLVM 3.1 seems to have improved the siutation, but I'm running into a new error. Here is the error I get when trying to build GHC 7.6.1 from 7.4.1 ===--- building final phase make -r --no-print-directory -f ghc.mk phase=final all LD libraries/ghc-prim/dist-install/build/HSghc-prim-0.3.0.0.o /usr/bin/ld: error: libraries/ghc-prim/dist-install/build/cbits/debug.o uses VFP register arguments, libraries/ghc-prim/dist-install/build/HSghc-prim-0.3.0.0.o does not /usr/bin/ld: failed to merge target specific data of file libraries/ghc-prim/dist-install/build/cbits/debug.o /usr/bin/ld: error: libraries/ghc-prim/dist-install/build/cbits/longlong.o uses VFP register arguments, libraries/ghc-prim/dist-install/build/HSghc-prim-0.3.0.0.o does not /usr/bin/ld: failed to merge target specific data of file libraries/ghc-prim/dist-install/build/cbits/longlong.o /usr/bin/ld: error: libraries/ghc-prim/dist-install/build/cbits/popcnt.o uses VFP register arguments, libraries/ghc-prim/dist-install/build/HSghc-prim-0.3.0.0.o does not /usr/bin/ld: failed to merge target specific data of file libraries/ghc-prim/dist-install/build/cbits/popcnt.o make[1]: *** [libraries/ghc-prim/dist-install/build/HSghc-prim-0.3.0.0.o] Error 1 I get similar errors when building GHC 7.4.1 (patched with http://hackage.haskell.org/trac/ghc/attachment/ticket/5914/0001-add-support…) Any of you encountered this problem before? -- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''

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any successfull ghc registerised builds on arm?
by Nathan Hüsken 26 Jan '13

26 Jan '13

In a different thread (Error building ghc on raspberry pi): On 01/08/2013 12:27 PM, Thijs Alkemade wrote:(...) > > I did eventually finish building stage2, but the final executable segfaulted on start. > I haven't investigated much why that happened, the days it takes to rebuild it just > made me give up. Was that an registerised or unregisterised build? Did anyone succesfully build ghc on an arm system which produces non crashing executables? I am asking, because I build a arm-linux-androideabi cross compiler, but the executables crash. Only in an unregisterised build, they work. So I wonder if it is a general arm problem or has to do with android. Thanks! Nathan

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GHCJS, JavaScript, cross-platform typechecking with the GHC API and primops
by Luite Stegeman 25 Jan '13

25 Jan '13

hi all, I've been working on GHCJS [1] for a while and am trying to get it to work on 64 bit GHC. A quick background: GHCJS uses the GHC API to generate STG, which it then translates to JavaScript. It uses slightly patched versions of the integer-gmp, base and ghc-prim libraries and supports many GHC features, including arrays and threading. All JavaScript numbers are essentially double precision floating point. With some tricks (using bitwise operators) it's possible to get reasonable 32 bit integer emulation out of it, but emulating 64 bit integers would be very slow. Therefore, if we compile Haskell to JavaScript, it should really be treated as a 32 bit target. Now this is a problem, with GHC 7.6 and lower, generated STG depended on the word size of the host, so it was simply impossible to do this with a 64 bit host. In HEAD, wORD_SIZE_IN_BITS is now in DynFlags, so I decided to have another go. I'm aiming for the following procedure to install GHCJS and build a package: # cabal install ghcjs -- installs `ghcjs`, `ghcjs-boot`, `ghcjs-pkg`, `ghcjs-cabal` # ghcjs-boot -- build ghc-prim, integer-gmp, base for GHCJS and register them in its package db # ghcjs-cabal install myPackage -- cabal wrapper that uses ghcjs instead of ghc GHCJS instructs the GHC API to build 32 bit code [2] and sets preprocessor definitions so that libraries also expect 32 bit code. Library patches include PrimOpWrappers in ghc-prim, which is generated from the 32 bit primops. But here's the problem: When typechecking PrimOpWrappers, the GHC API appears to use its own built-in types for everything in GHC.Prim, and there are differences between 32 bit and 64 bit (for example popCnt64# :: Word64# -> Word# on 32 bit, :: Word# -> Word# on 64), so you get lots of errors. Now I'm wondering, is there a way around this, or would it be reasonable to modify GHC to somehow have the primop types in DynFlags, instead of them being hardcoded in the compiler? luite [1] https://github.com/ghcjs/ghcjs (I'm mostly working in the Gen2 branch, an experimental faster code generator) [2] https://github.com/ghcjs/ghcjs/blob/gen2/src-bin/Compiler/Main.hs#L345

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ghc passing -undef to preprocessor and thereby eliminating OS specific defines
by Nathan Hüsken 24 Jan '13

24 Jan '13

Hey, I am trying to adapt some code in the libraries when compiling for android (i.E. because some things are different on android to other posix systems). So in C code I would just do "#ifdef __ANDROID__". While in the *.h and *.c files it seems to work, it does not work in *.hs files. I noted that the preprocessor is run like this: arm-linux-androideabi-gcc -E -undef -traditional -fno-stack-protector -DTABLES_NEXT_TO_CODE The "-undef" parameter is causing the __ANDROID__ define to be removed. Does it make sense to pass "-undef" to the preprocessor? Any other Ideas how I could adapt the code for android? Thanks! Nathan

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Cabal and cross compilation
by Nathan Hüsken 23 Jan '13

23 Jan '13

Hey, I am working on getting ghc to cross compile to android. When trying to get haskeline to compile. I want to change the cabal file such that it sets a flag when compiling for android. For that I changed cabal so that it recognizes android as a OS. But cabal seems to get its os information from System.Info.os, and from what I can tell this always returns the host os and not the target os. Am I getting this right, is cabal unaware of the target os? How can we change this? Regards, Nathan

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