status of template haskell + cross compiling plans for 7.8?

Luke Iannini lukexipd at
Fri Jun 14 11:04:50 CEST 2013

Yo Carter,
I worked with Stephen Blackheath earlier this year to help get his awesome
iOS patches for Cabal and GHC into mainline and am also super keen to see
TH support for cross compiling (which I think he is as well). So thanks for
raising the issue, and just want to say that I'd be pumped to assemble and
be a part of a team to work on this.


On Thu, Jun 13, 2013 at 11:59 PM, Carter Schonwald <
carter.schonwald at> wrote:

> Which raises the question then: what would be needed to make this happen
> by 7.10, if not sooner?
> naively, I'd imagine one part of the challenge is that Template haskell
> induces needing a ghc that can build libraries for *BOTH* host and target,
> because we have arbitrary execution at Template Haskell time, right?
> So does that mean fixing up GHC's architecture so that it can be built
> with support for more than 1 target? (or at least running libs on *host* in
> GHCI but otherwise compiling them for target? )
> What would be needed in the restricted case of "We just want TH for our
> cross compiler" rather than "general multi target goodness"?
> Because If I squint, it sort of sounds like the cross compiler would need
> to be Stage 2, and that the UNsound but simplest approach would then be to
> take the various "libways", and produce both host and target variants as
> appropriate (or that "build HOST Way" has to explicitly flagged).  I"m not
> sure what implications this or another approach would have on all the
> various build tooling needed etc etc.
> This is me just  thinking out loud / trying to understand *why* and whats
> needed, and how complex the work would be to do it well, or at least
> decently in a way that *improves* (or doesn't complicate much more) the
> associated parts that would need to be fixed up.
> Basically: whats needed to make cross compiler  GHC first class haskell
> wrt TH support? (I imagine that its not worth working on till the new TH
> work lands / stabilizes, but id like to understand what work has to be done
> to lead up to it).
> (if I can figure out ways I can directly or indirectly support such work
> happening, subject to having the time and/or resources over the next year,
> i'd like to try and do so)
> -Carter
> On Thu, Jun 13, 2013 at 8:28 PM, Manuel M T Chakravarty <
> chak at> wrote:
>> Carter,
>> As you can imagine, I would be extremely happy about cross-compilation
>> support for TH. However, I don't know of anybody working on it at the
>> moment, unfortunately.
>> Manuel
>> Carter Schonwald <carter.schonwald at>:
>> > 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
>> > _______________________________________________
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>> >
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