[Nix-dev] How to build a Haskell binding to a C++ library (OpenCV) on OS X

[Vincent Laporte]

Hi,

Notice that if you replace the two occurrences of ‘g++’ by ‘clang++’ in
the file ‘opencv/Setup.hs’, then ‘nix-build’ succeeds.

This issue might be reported upstream: they apparently need a configure
step to select the correct name of the C++ compiler.

The following patch also appears to make ‘nix-build’ work.

Regards,
--
Vincent.

```
diff --git a/opencv/Setup.hs b/opencv/Setup.hs
index 031daa1..3c92176 100644
--- a/opencv/Setup.hs
+++ b/opencv/Setup.hs
@@ -3,6 +3,6 @@ import System.Environment ( getArgs )

 main = do
     args <- getArgs
-    let args' | "configure" `elem` args = args ++ ["--with-gcc","g++",
"--with-ld","g++"]
+    let args' | "configure" `elem` args = args
               | otherwise               = args
     defaultMainArgs args'
diff --git a/opencv/opencv.nix b/opencv/opencv.nix
index a28674c..80ed995 100644
--- a/opencv/opencv.nix
+++ b/opencv/opencv.nix
@@ -103,8 +103,8 @@ mkDerivation ({
   libraryPkgconfigDepends = [ opencv3 ];

   configureFlags =
-    [ "--with-gcc=g++"
-      "--with-ld=g++"
+    [ "--with-gcc=${stdenv.cc}/bin/c++"
+      "--with-ld=${stdenv.cc}/bin/c++"
     ];

   hardeningDisable = [ "bindnow" ];
```