Hello Albert,
Thanks for taking the time to help me fix this package stuff. So I wiped out my package.conf.d/ and tried to reinstall my stuff. Installing template-haskell 2.5.0.0 is ok (2.6 is not, fails to compile on ghc 7.0.3) but then:

D:\projets\>ghc --make -package ghc main
<command line>: cannot satisfy -package ghc
    (use -v for more information)

I suspect I really *do* have to reinstall haskell-platform. Here is the output of ghc-pkg list -v:

using cache: C:\Documents and Settings\abailly\Application Data\ghc\i386-mingw32-7.0.3\package.conf.d\package.cache
using cache: D:/Program Files/Haskell Platform/2011.2.0.1\lib\package.conf.d\package.cache
D:/Program Files/Haskell Platform/2011.2.0.1\lib\package.conf.d:
    Cabal-1.10.1.0 (Cabal-1.10.1.0-55f781465ee9f32289755ad706c71f0f)
    GLUT-2.1.2.1 (GLUT-2.1.2.1-2d30997b9a19d27be388572e75af52bf)
    HTTP-4000.1.1 (HTTP-4000.1.1-267a332938fa742ba5a5d59de0b46d60)
    HUnit-1.2.2.3 (HUnit-1.2.2.3-102fbfbd594cd6d38461f5c68d880996)
    OpenGL-2.2.3.0 (OpenGL-2.2.3.0-a58ce3ad6070e6b7932a3e779be57f75)
    Win32-2.2.0.1 (Win32-2.2.0.1-26cf39fdf591bdac61b11d5a443c62ab)
    array-0.3.0.2 (array-0.3.0.2-8e9cd0144e87fa9cc86cc9031631c4f3)
    base-4.3.1.0 (base-4.3.1.0-f520cd232cc386346843c4a12b63f44b)
    bin-package-db-0.0.0.0 (bin-package-db-0.0.0.0-97d865e5935b41538bcb29fc1040ae7d)
    bytestring-0.9.1.10 (bytestring-0.9.1.10-cd85f14e02463c02ba4c77d7adcdb54f)
    cgi-3001.1.7.4 (cgi-3001.1.7.4-659440ce11c2975fd9c9c471a1e8ff3b)
    containers-0.4.0.0 (containers-0.4.0.0-18deac99a132f04751d862b77aab136e)
    deepseq-1.1.0.2 (deepseq-1.1.0.2-09b3aed0c4982bbc6569c668100876fa)
    directory-1.1.0.0 (directory-1.1.0.0-3a2367d72569467a8af8a231656ff1b8)
    extensible-exceptions-0.1.1.2 (extensible-exceptions-0.1.1.2-d8c5b906654260efd7249f497d17a831)
    ffi-1.0 (builtin_ffi)
    fgl-5.4.2.3 (fgl-5.4.2.3-595811d6eabb1e1768685703ea66e982)
    filepath-1.2.0.0 (filepath-1.2.0.0-f132e9f7703da4e20a47ff2b9acf1ea1)
    (ghc-binary-0.5.0.2 (ghc-binary-0.5.0.2-aba2b5dca5546ea1a972188de48f87b5))
    ghc-prim-0.2.0.0 (ghc-prim-0.2.0.0-e1f7c380581d61d42b0360d440cc35ed)
    haskell-src-1.0.1.4 (haskell-src-1.0.1.4-7428a8c9049cd6bf5abdc0bbd2d417c5)
    (haskell2010-1.0.0.0 (haskell2010-1.0.0.0-53d9cd65595c551eea0c0269f534b5e0))
    haskell98-1.1.0.1 (haskell98-1.1.0.1-35ec26bae828637c1638c8be441b3d68)
    hpc-0.5.0.6 (hpc-0.5.0.6-481dbb43fb624c21ad3bb9434675e3ac)
    html-1.0.1.2 (html-1.0.1.2-a494249f98a0f38b1a8db28bc70f8b0b)
    integer-gmp-0.2.0.3 (integer-gmp-0.2.0.3-91607778cf3ae8f3948a50062b4f8479)
    mtl-2.0.1.0 (mtl-2.0.1.0-fb4d1695269b74308c1517c06b76e6e8)
    network-2.3.0.2 (network-2.3.0.2-47657e39a6118a978d9f443d72e85d4a)
    old-locale-1.0.0.2 (old-locale-1.0.0.2-6e2a3c0744e8cf4e0ac2d4e58659f7b5)
    old-time-1.0.0.6 (old-time-1.0.0.6-445ce39cbcebd38069c25c0f383b728d)
    parallel-3.1.0.1 (parallel-3.1.0.1-6eaa564e1ef1537bc88ad1fea6c90fe2)
    parsec-3.1.1 (parsec-3.1.1-9da59b00c02e52f9f62f3c87c7e0e2ec)
    pretty-1.0.1.2 (pretty-1.0.1.2-abc7c632374e50e1c1927987c2651f0f)
    process-1.0.1.5 (process-1.0.1.5-b3dded8e54a2e13d22af410bdcfafff4)
    random-1.0.0.3 (random-1.0.0.3-1abde37180be5476311abeefe300abc2)
    regex-base-0.93.2 (regex-base-0.93.2-9e1b027c41dbec856469a30982495bb9)
    regex-compat-0.93.1 (regex-compat-0.93.1-31c61fe0aee45e8a9853edf7a844f74e)
    regex-posix-0.94.4 (regex-posix-0.94.4-f5eb628ea5dae5f91552d5ea0e26359d)
    rts-1.0 (builtin_rts)
    stm-2.2.0.1 (stm-2.2.0.1-57e291244ee02349552a4f79caeb4ffe)
    syb-0.3 (syb-0.3-8db7bc4339a1cb8a6f2a46c40447ef0b)
    text-0.11.0.6 (text-0.11.0.6-398a3f02891247aea46662fc7379c4a5)
    time-1.2.0.3 (time-1.2.0.3-74ef6ac31cee9aec02b036978af002d2)
    transformers-0.2.2.0 (transformers-0.2.2.0-2fe7b735c63a6cbe8724038d8e4d812a)
    xhtml-3000.2.0.1 (xhtml-3000.2.0.1-ace31b2e48c396e565655b0f34f5d2b7)
    zlib-0.5.3.1 (zlib-0.5.3.1-5fbdf714525b76e0e601c2ffb25f2044)

C:\Documents and Settings\abailly\Application Data\ghc\i386-mingw32-7.0.3\package.conf.d:
    QuickCheck-2.4.1.1 (QuickCheck-2.4.1.1-04d68679694a517ba23022a4c6bc1cde)
    ghc-paths-0.1.0.8 (ghc-paths-0.1.0.8-be391faf057d651dbb92b73671fe9eee)
    template-haskell-2.5.0.0 (template-haskell-2.5.0.0-87f4f416a22a910e480ac9f269479a5f)
    utf8-string-0.3.7 (utf8-string-0.3.7-dcbcb8de655cdfe1c4c28c094f8c6799)

Thanks again,
Arnaud

On Sat, Aug 27, 2011 at 8:59 PM, Albert Y. C. Lai <trebla@vex.net> wrote:

You have too many instances of template-haskell. The important parts are:

package ghc-7.0.3-fc75cf67c86ba2c0d64b07024a18d3b4 is unusable due to missing or recursive dependencies:
template-haskell-2.5.0.0-7d9b1443ac5ab69e5ed705a487990deb

package template-haskell-2.5.0.0-7d9b1443ac5ab69e5ed705a487990deb is shadowed by package template-haskell-2.5.0.0-87f4f416a22a910e480ac9f269479a5f

and in "ghc-pkg list -v":

D:/Program Files/Haskell Platform/2011.2.0.1\lib\package.conf.d:

template-haskell-2.5.0.0 (template-haskell-2.5.0.0-7d9b1443ac5ab69e5ed705a487990deb)

C:\Documents and Settings\abailly\Application Data\ghc\i386-mingw32-7.0.3\package.conf.d:

template-haskell-2.5.0.0 (template-haskell-2.5.0.0-87f4f416a22a910e480ac9f269479a5f)

I don't know how you got to this unsafe state. But my article explains what's wrong with it. (Though my example has different version numbers on top of different ABI hashes).

The user instance of template-haskell (87f4f416a22a910e480ac9f269479a5f) is getting into the way. Lose it by doing "ghc-pkg unregister --user template-haskell" on it. Oh, it will complain about breaking other packages; well, lose them too.

(Or go one step further and lose all of C:\Documents and Settings\abailly\Application Data\ghc\i386-mingw32-7.0.3\package.conf.d which means losing all user packages.)

(Reinstalling haskell platform changes nothing, as long as some user package gets into the way.)