The issue that we hit sooner than this is that when we build a cross-compiler, we build all the libs for the target platform and not the host platform (see http://hackage.haskell.org/trac/ghc/wiki/CrossCompilation).  So to make TH work, we have to change the way we build cross compilers, and make the build system able to build and install two sets of libs.  This is probably a big job.

I think it might be possible to avoid needing a multi-target GHC, as long as you have two identical GHCs, one that produces code for the host platform (host-GHC) and one for the target platform (cross-GHC).  You compile all the code once with host-GHC, and then again with the cross-GHC, the second time using the .o files produced by host-GHC to run the TH code.

Cheers,
        Simon

On 17/06/13 14:52, Simon Peyton-Jones wrote:

I have not been following the details of this debate, but there is a
good reason why TH doesn’t work on a cross compiler. Specifically,
suppose module M imports module X, which defines a function mkD that M
calls in a splice, thus $(mkD “wobble”).

Currently, we compile X to X.o, and when compiling M we dynamically link
X.o (and all the other libraries it relies on) into GHC so that we can
call foo.  Obviously X.o has to be runnable on the machine doing the
compiling, so if X.o is for some other architecture that’s not going to
work.

There is no reason in principle why one could not compile X into
X.bytecode (along with all its dependencies), where X.bytecode is
architecture independent. Then X.bytecode could be interpreted on any
platform.  But GHC has no mechanism for doing this at all.   I’ve always
take the view that if you want X.bytecode, you may as well load X.hs and
translate it into bytecode.  A bit slower, to be sure, but maybe fast
enough.  But don’t forget those libraries.

Anyway that’s the state of play.   Have fun!

Simon

*From:*ghc-devs-bounces@haskell.org
[mailto:ghc-devs-bounces@haskell.org] *On Behalf Of *Carter Schonwald
*Sent:* 13 June 2013 22:44
*To:* ghc-devs@haskell.org
*Subject:* status of template haskell + cross compiling plans for 7.8?

Hey All,

Whats the story planned for template haskell + cross compiler support
come ghc 7.8?

I understand theres a lot of Template Haskell design underway, some of
which will help support tools like Manuel's Inline-Objective-C work.
Does this mean that factored out within this reorganization is a better
story for cross compilation?

Especially since one kill "app" for the Inline-Objective-C template
haskell work would be writing IOS applications. Though I guess that also
touches on the need to sort out supporting "FAT" ARM binaries too, right?

This intersects with a few different large subsets of tickets, so i'm
not sure if any single ticket is the right fora for this question.

thanks!

-Carter

_______________________________________________
ghc-devs mailing list
ghc-devs@haskell.org
http://www.haskell.org/mailman/listinfo/ghc-devs

_______________________________________________
ghc-devs mailing list
ghc-devs@haskell.org
http://www.haskell.org/mailman/listinfo/ghc-devs