[Haskell-cafe] What's wrong with "cgi-undecidable"?

[Matthew Brecknell]

> http://darcs.haskell.org/packages/cgi-undecidable/
> 
> There only 3 or 4 lines of source code, but it can't be installed.
> 
> The ghc version is 6.6 .
> 
> Undecidable.hs:23:0:
>     Duplicate instance declarations:
>       instance [overlap ok] (MonadTrans t, MonadCGI m, Monad (t m)) =>
>                             MonadCGI (t m)
>         -- Defined at Undecidable.hs:23:0
>       instance [overlap ok] (MonadTrans t, MonadCGI m, Monad (t m)) =>
>                             MonadCGI (t m)
>         -- Defined in Network.CGI.Monad

You probably have an old version of the cgi package, which contained the
above instance declaration before it was moved to cgi-undecidable. Hence
the "duplicate instance declaration" message. Try updating your cgi
package first.