More specifically, section "2.2.2 Moving GHC Around" indicates that the entire GHC tree can be freely moved around "just by copying the c:/ghc/ghc-version directory" (although it is necessary "to fix up the links in 'Start/All Programs/GHC/ghc-version'" if this is done); however, this information is not evident from the information provided by the Windows installer. This information initially led me to conclude that uninstalling the previous version wasn't necessary to upgrade; without this information, a new user may not be able to determine whether uninstalling a previous version is necessary to upgrade, and could make upgrading more confusing.
I've added a section "Relocating a GHC installation" to the wiki:
http://hackage.haskell.org/trac/ghc/wiki/Building/Installing#RelocatingaGHCi...
Relocation on Windows is currently slightly impeded if you're using the Haskell Platform's GHC http://trac.haskell.org/haskell-platform/ticket/19
I think the rest could be solved by adding a note on the Windows section of the download page to the effect that "This installer will not overwrite previous installed versions of GHC, with the exception that the default handler for .lhs and .hs files will point to the latest installed version". Ian, would you like to add this to the download page?
For quite some time now, http://darcs.haskell.org/ghc/distrib/ghc.iss has had this comment (in line with #916): ; this does _not_ follow the "play nice" proposal ; future version should The current version will needlessly assign a different file type, leaving Hugs in the cold (unless you install WinHugs last, which removes the GHCi association..) and overwrite the handlers associated with ghc_haskell (so if you want to use multiple versions of GHCi, you have to add them back in manually). See also: http://hackage.haskell.org/trac/ghc/ticket/916 http://haskell.org/haskellwiki/Installers http://trac.haskell.org/haskell-platform/ticket/6#comment:12 The solution could be as simple as all distributors agreeing on a single haskell file type (so that WinHugs won't switch out the Haskell Platform bindings, and vice versa), and then not mangling the default "verbs" 'open' and 'edit', but to use non-standard verbs like open_with_GHCi-6.10.3, so that Haskell installers add, rather than replace, functionality, as agreed on in that haskellwiki page. Works in Windows XP, and avoids Haskell installer ping-pong http://projects.haskell.org/pipermail/haskell-platform/2009-May/000154.html The MSDN docs seem to be in upheaval at the moment, so I can't verify that this [1] was the most useful documentation link - I think that, before Windows XP, there was no support for non-standard verbs, so on older Windows versions, the current bad system might have to be used as a fallback, but that is no reason to use it on current versions, several years after agreement): Claus [1] http://msdn.microsoft.com/library/en-us/shellcc/platform/shell/programmersgu... [2] http://blogs.msdn.com/oldnewthing/archive/2007/04/30/2332224.aspx 'The default verb is not necessarily "open"'