Added standalone diagram-builder haskell package.

Simple wrapper over `haskellng`'s `diagram-builder`
package that allows for simpler install.

pkgs/tools/graphics/diagrams-builder/default.nix

@@ -0,0 +1,43 @@
+/*
+  If user need access to more haskell package for building his
+  diagrams, he simply has to pass these package through the
+  extra packages function as follow in `config.nix`:
+  
+  ~~~
+  diagrams-builder.override {
+    extraPackages = self : [myHaskellPackage];
+  }
+  ­~~~
+*/
+
+{ stdenv, ghcWithPackages, makeWrapper, diagrams-builder, extraPackages ? (self: []) }:
+let
+  # Used same technique as for the yiCustom package.
+  w = ghcWithPackages 
+    (self: [ diagrams-builder ] ++ extraPackages self);
+  wrappedGhc = w.override { ignoreCollisions = true; };
+  ghcVersion = w.version;
+in
+stdenv.mkDerivation {
+  name = "diagrams-builder";
+  buildInputs = [ makeWrapper ];
+  buildCommand = ''
+    makeWrapper \
+    "${diagrams-builder}/bin/diagrams-builder-svg" "$out/bin/diagrams-builder-svg" \
+      --set NIX_GHC ${wrappedGhc}/bin/ghc \
+      --set NIX_GHC_LIBDIR ${wrappedGhc}/lib/ghc-${ghcVersion}
+
+    makeWrapper \
+    "${diagrams-builder}/bin/diagrams-builder-cairo" "$out/bin/diagrams-builder-cairo" \
+      --set NIX_GHC ${wrappedGhc}/bin/ghc \
+      --set NIX_GHC_LIBDIR ${wrappedGhc}/lib/ghc-${ghcVersion}
+
+    makeWrapper \
+    "${diagrams-builder}/bin/diagrams-builder-ps" "$out/bin/diagrams-builder-ps" \
+    --set NIX_GHC ${wrappedGhc}/bin/ghc \
+    --set NIX_GHC_LIBDIR ${wrappedGhc}/lib/ghc-${ghcVersion}
+  '';
+  # Will be faster to build the wrapper locally then to fetch it from a binary cache.
+  preferLocalBuild = true;
+  meta = diagrams-builder.meta;
+}

pkgs/top-level/all-packages.nix

@@ -764,6 +764,10 @@ let
 
   ddate = callPackage ../tools/misc/ddate { };
 
+  diagrams-builder = callPackage ../tools/graphics/diagrams-builder {
+    inherit (haskellngPackages) ghcWithPackages diagrams-builder;
+  };
+
   direnv = callPackage ../tools/misc/direnv { };
 
   discount = callPackage ../tools/text/discount { };