If you landed here, you are probably new to Haskell and somehow ran into this error message while installing something using cabal:
"Unsupported extension: LambdaCase"
You’re probably using a version of Haskell that’s too old canadian free slots (like whatever came on your default *nix installation).
LambdaCase was added in 7.6.1. It is a purely syntactic extension.
You should use Haskell Platform instead of whatever ghc you’ve got on your machine now.
If you’re running Ubuntu 12.04 (Precise) or earlier (“cat /etc/lsb-release” to find out what version you are running), your package manager ships with a Haskell Platform that includes a GHC that is too old. If that’s the case, you can install GHC directly.
Thanks to Iceland_jack, jle`, and kqr in #haskell for pointing me in the right direction when I ran into this.