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Subject: Re: ANN: Happstack 0.4.1
From: Erik Hesselink <hessel...@gmail.com>
To: HAppS <happs@googlegroups.com>
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On Dec 22, 4:33=A0am, Antoine Latter <aslat...@gmail.com> wrote:
> On Mon, Dec 21, 2009 at 6:31 AM, =A0<jer...@n-heptane.com> wrote:
> > Hello,
>
> > That sort of missing symbol error at link time is often (but not always=
) a
> > sign that some libraries got recompiled but not others. So there are
> > references to the old symbol names hanging around.
>
> > I would try to ghc-pkg unregister syb-with-class and everything that de=
pends
> > on it, and then try cabal install happstack again.
>
> I'm pretty well stumped at this point. I've cleared off everything and
> gone up to GHC 6.12 HEAD, and a 'cabal install happstack-data' gives
> me the same symbol not defined error in Happstack.Data.Xml.Base.
>
> But here's the spooky part, if I run it by hand like so:
>
> ghc --make src/Happstack/Data/Xml/Base.hs
> src/Happstack/Data/Default.hs src/Happstack/Data/
> DeriveAll.hs src/Happstack/Data/Normalize.hs src/Happstack/Data/Migrate.h=
s
>
> after resolving issues due to CPP not being run, everything runs to
> completion, no errors. Also, the list of things we're pulling in
> during the template-haskell execution is much smaller (see bellow).

I've found that if I log the command cabal executes (cabal install -v)
and execute that by hand, it doesn't work. However, if I remove the -O
flag from there, it _does_ work. So a workaround is this:

cabal install -O0 happstack-data

I have no idea _why_ it is failing with optimizations on, though.

> Has anyone seen this, where template-haskell behaves different when
> run from cabal-install (or Setup.hs) than from ghc --make (or ghci)?

Yes, I have seen that before, but in that case, I think it was the ghc
linker doing something different from the standard linker, possibly
related to GHC bug 3333 [1]. I think every bug or limitation that
applies to ghci also applies to cabal if you're using template haskell
(at least that's my suspicion).

[1] http://hackage.haskell.org/trac/ghc/ticket/3333

Erik