You've got two options:

1) (the easy way)

rm -rf ~/.ghc ~/.cabal

cabal update
cabal install scotty

2) (the hard way, ghc 7.6+ only)

Use a sandbox!

cd path/to/my/project/that/uses/scotty

cabal sandbox init
cabal install --only-dependencies -j # make sure scotty is a dependency of your project

cabal configure

cabal build

3) use cabal-dev. similar to using sandboxes, but I don't have it any more so can't give you a step-by-step.

On Tue, Nov 26, 2013 at 7:34 PM, Thiago Negri <evohunz@gmail.com> wrote:

I don't know what to do. :-(
I can't install scotty or yesod.

$ cabal install scotty
cabal: Could not resolve dependencies:
trying: scotty-0.5.0 (user goal)

trying: base-4.7.0.0/installed-dc1... (dependency of scotty-0.5.0)
trying: wai-extra-1.3.4.6 (dependency of scotty-0.5.0)
trying: stringsearch-0.3.6.4 (dependency of wai-extra-1.3.4.6)
rejecting: stringsearch-0.3.6.4:-base3 (conflict:

base==4.7.0.0/installed-dc1..., stringsearch-0.3.6.4:base3 => base>=2 && <3)
rejecting: stringsearch-0.3.6.4:+base3 (conflict:

base==4.7.0.0/installed-dc1..., stringsearch-0.3.6.4:base3 => base>=3 && <4)

Backjump limit reached (change with --max-backjumps).

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