Friends I want to thank everyone who has responded - very helpful! Thanks to your help I am making progress * I re-installed msys64 from scratch, this time following the instructions on the GHC wiki rather than the msys2 page. By doing update-core; then pacman -Su; then pacman -Su again, I got a clean install. Very good! Getting a shell between each step is tricky. o The first shell is gotten with mingw64.bat o After update-core, that file is gone; you have to use msys2_shell.cmd I think o After pacman -Su we get mingw64.exe, which we can use thereafter. * My slow-start problem appears to have gone away. I adopted the fix from you may be hitting a long standing issue some computers have in which the domain controller is being hit for every invocation of commands, causing a slowdown https://github.com/Alexpux/MSYS2-packages/issues/138 , Solution 2 from https://gist.github.com/k-takata/9b8d143f0f3fef5abdabhttps://na01.safelinks.protection.outlook.com/?url=https%3a%2f%2fgist.github.com%2fk-takata%2f9b8d143f0f3fef5abdab&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7cdd4588e2f3ff499367c308d39f535acd%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=KQFg%2f83I5Vj%2bS4ivgSvAI%2bpt3A04ulMjbO%2bbIrsb%2btQ%3d seems to fix it for most people. I am not absolutely certain that was the problem, but things seem ok now. I also excluded c:/msys64 from my antivirus check. * Emacs too is now working normally. Hurrah So that's all good. Now I'm stuck on the windows tarballs download thing. I get configure: Checking for Windows toolchain tarballs... configure: Extracting Windows toolchain from archives (may take a while)... File not found - *.tar.xz I tried both the things described on the wikihttps://ghc.haskell.org/trac/ghc/wiki/Building/Preparation/Windows: Pacman -R mingw-w64-x86_64-curl error: target not found: mingw-w64-x86_64-curl For the other I did the two mkdir things, and tried ./configure again, but got the same error message as above. So I'm stuck again, but further forward. Can you advise me? Thanks! Simon