I have installed Haskell Platform 2012 in Windows 7. I write in the console cabal update and I take a message that there is a new version of cabal. I write cabal install cabal-install . After installation finishes it tells me that the cabal has been installed in C:\username\AppData\Roaming\cabal. So when I do cabal update again I am taking the same message that I have to install the new version of cabal. I have tried to change the cabal directory from the config file but cabal ignores the config file. Is Haskell working only on Unix? Thanks
The problem is that the cabal executable that came with Haskell Platform gets picked up instead of the one that you installed.
You need to edit the value of the PATH environment variable and place %AppData%\cabal\bin before %PROGRAMFILES%\Haskell Platform\...\bin so that it's given higher priority.
You need to add C:\username\AppData\Roaming\cabal (or whatever directory now has the cabal executable -- use e.g. dir or your favorite file manager to verify that you have the right place) to your %PATH% environment variable and restart your command prompt.
The error message is incomplete. Install cabal-install globally as:
cabal install cabal-install --global
来源：https://stackoverflow.com/questions/15461085/how-to-configure-cabal-in-windows-7