Add setAttrByPath:

- used to defined an attribute with its path as a list of attribute names.

svn path=/nixpkgs/trunk/; revision=17480

pkgs/lib/attrsets.nix

@@ -22,6 +22,14 @@ rec {
       then attrByPath (tail attrPath) default (getAttr attr e)
       else default;
 
+  /* Return nested attribute set in which an attribute is set.  For instance
+     ["x" "y"] applied with some value v returns `x.y = v;' */
+  setAttrByPath = attrPath: value:
+    if attrPath == [] then value
+    else listToAttrs [(
+      nameValuePair (head attrPath) (setAttrByPath (tail attrPath) value)
+    )];
+
       
   /* Backwards compatibility hack: lib.attrByPath used to be called
      lib.getAttr, which was confusing given that there was also a