Hi, I just successfully built GHC on Windows. Last time I tried (5 years ago) it took days. This time, it took hours, plus a bit of waiting for a Windows specific breakage to be fixed. I made a log of what happened, what confused me, what wasn't clear etc - hopefully these provide suggestions for improving the wiki (if my thoughts are actually correct). The worst aspect is that the Windows wiki page has 6 sets of instructions, with no obvious way to pick the right one - everything else was pretty minor. Thanks, Neil My first step was to Google "build ghc on windows", which took me to https://ghc.haskell.org/trac/ghc/wiki/Building/Preparation/Windows "The instructions are current for GHC 7.6" - so they are not current. "Other documentation for Windows includes:" - here are 5 alternate links, any of which may be better/worse than this one. I have no way to tell. As a piece of documentation, giving the uninformed user 6 options with no sensible way to make a decision is awful. Simon PJ had said "MSYS2" works well, so I clicked that one. Even though it appears to be the "wrong" one according to the wiki. Is it the correct one? If so, replace the Windows page with it. If not, perhaps indicate which one is. "It should get you running in ~5 minutes, modulo download speeds." - nice! It's a long way from being true, since you also need to include extraction times and build times (which on my machine far outweight download times). There were also enough hiccups that it took me about an hour of clicking/typing, excluding the Windows specific bug I ran into. If I have 64bit OS, should I pick 64bit Windows? Or only if I want to develop 64bit Windows, which isn't the default? Fortunately my machine is old enough to be 32 bits so I didn't have the difficult question. It's far easier to edit the PATH file manually with $ cygpath -w ~, which returns C:\msys32\home\Neil, than to echo stuff to it. In particular, if you echo anything wrong, you need to edit it anyway. "Do not install python, python2 or gcc!" - it's not entirely clear how to achieve that. It installed gcc-libs, is that a problem? I'd have liked a better "check" step, e.g. run "gcc --version", "ghc --version" and exactly what I should expect, what indicates a problem etc. e.g what should i be on the lookout for to say Python doesn't build. I followed the step to upgrade my system, but it failed: :: Starting full system upgrade... :: Replace msys2-base with msys/filesystem? [Y/n] (55/55) checking for file conflicts [######################] 100% error: failed to commit transaction (conflicting files) bash-completion: /etc/profile.d/bash_completion.sh exists in filesystem coreutils: /etc/DIR_COLORS exists in filesystem ca-certificates: /etc/pki/ca-trust/extracted/java/cacerts exists in filesystem ca-certificates: /etc/pki/ca-trust/extracted/openssl/ca-bundle.trust.crt exists in filesystem ca-certificates: /etc/pki/ca-trust/extracted/pem/email-ca-bundle.pem exists in filesystem ca-certificates: /etc/pki/ca-trust/extracted/pem/objsign-ca-bundle.pem exists in filesystem ca-certificates: /etc/pki/ca-trust/extracted/pem/tls-ca-bundle.pem exists in filesystem filesystem: /etc/profile.d/lang.sh exists in filesystem filesystem: /etc/profile.d/tzset.sh exists in filesystem filesystem: /etc/skel/.inputrc exists in filesystem filesystem: /mingw32_shell.bat exists in filesystem filesystem: /mingw64_shell.bat exists in filesystem filesystem: /msys2_shell.bat exists in filesystem grep: /usr/bin/egrep exists in filesystem grep: /usr/bin/fgrep exists in filesystem rebase: /autorebase.bat exists in filesystem Errors occurred, no packages were upgraded. I just ignored that, and continued, and that seemed to go OK... /ghc-7.6.3/ didn't work, I needed to go /c/ghc/ghc-7.6.3/ for the paths. Perhaps make it clear which are absolute paths, and which you have to edit. Perhaps you were hoping I'd symlink the GHC path? Any reason for the && commands in the final list of commands? isn't one per line cleaner? It also lets you retry the right bit when something fails. checking for version of happy... 1.18.4 configure: error: Happy version 1.19.4 or later is required to compile GHC. Nice - this was a useful check that made it easy to fix and continue. $ make -j3 + test -f mk/config.mk.old + cp -p mk/config.mk mk/config.mk.old touch -r mk/config.mk.old mk/config.mk + test -f mk/project.mk.old + cp -p mk/project.mk mk/project.mk.old touch -r mk/project.mk.old mk/project.mk 2 [main] make 6024 child_info_fork::abort: C:\msys32\bin\msys-unistring-2.dll: Loaded to different address: parent(0x250000) != child(0x7C0000) make: fork: Resource temporarily unavailable This error repeated. On a hunch I ran "autorebase.bat" from msys32, and restarted my shell, then it worked - I have no idea which fixed it. "inplace/bin/ghc-stage1.exe" -hisuf hi -osuf o -hcsuf hc -static -H32m -O -this-package-key haske_9y30zKcKDr9BxdhpktYrNk -hide-all-packages -i -ilibraries/haskeline/. -ilibraries/haskeline/dist-install/build -ilibraries/haskeline/dist-install/build/autogen -Ilibraries/haskeline/dist-install/build -Ilibraries/haskeline/dist-install/build/autogen -Ilibraries/haskeline/includes -optP-DUSE_GHC_ENCODINGS -optP-DMINGW -optP-include -optPlibraries/haskeline/dist-install/build/autogen/cabal_macros.h -package-key Win32_43THQMouBnk2wpnouztX1X -package-key base_ESD4aQEEWwsHtYJVc1BwtJ -package-key bytes_Kc0PyaputnzDnBdZW0y2Gv -package-key conta_ChF4XLXB9JmByIycPzerow -package-key direc_6qC0tVrFkqbBNeWAGS0s7g -package-key filep_34DFDFT9FVD9pRLLgh8IdQ -package-key trans_5jw4w9yTgmZ89ByuixDAKP -Wall -XHaskell98 -XForeignFunctionInterface -XRank2Types -XFlexibleInstances -XTypeSynonymInstances -XFlexibleContexts -XExistentialQuantification -XScopedTypeVariables -XGeneralizedNewtypeDeriving -XMultiParamTypeClasses -XOverlappingInstances -XUndecidableInstances -XCPP -XDeriveDataTypeable -XPatternGuards -O2 -no-user-package-db -rtsopts -odir libraries/haskeline/dist-install/build -hidir libraries/haskeline/dist-install/build -stubdir libraries/haskeline/dist-install/build -split-objs -c libraries/haskeline/dist-install/build/System/Console/Haskeline/Backend/Win32.hs -o libraries/haskeline/dist-install/build/System/Console/Haskeline/Backend/Win32.o librarieshaskelineSystemConsoleHaskelineBackendWin32.hsc:263:15: No instance for (Applicative (Draw m)) arising from the 'deriving' clause of a data type declaration Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself When deriving the instance for (Monad (Draw m)) I fixed that by applying the patch from https://ghc.haskell.org/trac/ghc/ticket/9598. With that, I could build to completion. An empty build (nothing to do) takes 1m50s which is a bit sad, but it does work. After all this there are exactly two things I want to know (both of which would be useful links from the bottom of the building on Windows page): * How do I update to the next day, resync and rebuild. In particular, should i sync-all or not (a link to another page is fine) * How do I run the tests.