I recently decided to try out a simple diagrams-cairo project on Windows 8 (x86_64) to discover that GHC (7.10.2, to be specific) acts rather bizarrely when dealing with external DLL dependencies. To start, I downloaded MSYS2 [1], installed the libraries needed for cairo and pango to work [2], installed diagrams-cairo [3], and tried running a simple diagrams program: module Main (main) where import Diagrams.Prelude import Diagrams.Backend.Cairo.CmdLine main :: IO () main = mainWith (circle 1 :: Diagram B) like so from MSYS2: runghc Cairo.hs -o circle.svg -w 400 And it worked. Hooray! Now, I normally use cmd.exe/PowerShell for most of my Windows command-line tasks, so later I tried invoking the above command on PowerShell, only to be greeted with an error message: $ runghc.exe .\Cairo.hs -o circle.svg -w 400 Cairo.hs: warning: _tzset from msvcrt is linked instead of __imp__tzset Cairo.hs: libcairo-2: The specified procedure could not be found. Cairo.hs: <command line>: can't load .so/.DLL for: libcairo-2.dll (addDLL: could not load DLL) PowerShell, alas, couldn't find libcairo-2.dll when MSYS2 had no trouble whatsoever. I realized that MSYS2 stores all of its MinGW-related DLL files in a special location (C:\msys64\mingw64\bin). This can be observed by running cygcheck on the executable: $ C:\msys64\usr\bin\cygcheck.exe .\Cairo.exe C:\Users\ryanscot\Documents\Hacking\Haskell\Cairo.exe cygcheck: track_down: could not find libcairo-2.dll cygcheck: track_down: could not find libglib-2.0-0.dll cygcheck: track_down: could not find libgobject-2.0-0.dll cygcheck: track_down: could not find libpango-1.0-0.dll cygcheck: track_down: could not find libpangocairo-1.0-0.dll ... After reading about DLL search paths in Windows [4], I got the impression that I could add C:\msys64\mingw64\bin to my PATH, and then executables would look for DLLs there. Adding C:\msys64\mingw64\bin to my PATH seemed to make cygcheck happy: $ C:\msys64\usr\bin\cygcheck.exe .\Cairo.exe C:\Users\ryanscot\Documents\Hacking\Haskell\Cairo.exe C:\msys64\mingw64\bin\libcairo-2.dll ... But invoking runghc Cairo.exe on PowerShell still fails with the same error message! For the life of me, I can't figure out what kind of sorcery MSYS2 is doing to make C:\msys64\mingw64\bin visible to the DLL search path from GHC. The only way I can trick PowerShell into seeing libcairo-2.dll is to (1) Copy libcairo-2.dll directly to C:\Windows\System32, or (2) Invoke SetDllDirectory("C:\msys64\mingw64\bin") [5] from a PowerShell startup script Neither of these options are very satisfying, since (1) has massive security implications, and (2) only works when you have one external DLL directory (if you called SetDllDirectory again with a different directory, it overrides the first one). I know there are folks out there who have managed to get diagrams working on Windows, so can someone let me know if I'm doing something wrong? Ryan S. ----- [1] http://msys2.github.io/ [2] pacman -S mingw-w64-x86_64-cairo mingw-w64-x86_64-pango 1.38.1-1 [3] cabal install diagrams-cairo [4] https://msdn.microsoft.com/en-us/library/ms682586.aspx#search_order_for_desk... [5] https://msdn.microsoft.com/en-us/library/windows/desktop/ms686203%28v=vs.85%...