ghc7 typing problem

[Christian Maeder]

Hi,

I've looked at:
http://hackage.haskell.org/trac/ghc/blog/LetGeneralisationInGhc7

but still have a problem with the attached program that fails with:

GHCi, version 7.1.20101010: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
[1 of 1] Compiling Main             ( HasKey.hs, interpreted )

HasKey.hs:17:10:
    Couldn't match type `key' with `key1'
      because this skolem type variable would escape: `key1'
    This skolem is bound by the instance declaration
    In the instance declaration for `Ord (Keyed x)'

at the final instance for Ord.

The original code comes from
http://hackage.haskell.org/packages/archive/uni-util/2.2.0.0/doc/html/Util-VariableSet.html

Cheers Christian
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