* Split lib/default.nix into several files, as it had become a big

mess.  Also cleaned up some functions:

  - foldl appeared broken (it recursively called fold).
  - Renamed logicalAND/logicalOR to and/or.
  - Removed listOfListsToAttrs, eqStrings: obsolete.
  - Removed isInList, which does the same thing as elem.
  - stringToCharacters: don't return a "" at the end of the list.
  - Renamed concatList to concat, as concatList (singular) is a
    misnomer: it takes two lists.  Likewise, renamed mergeAttr to
    mergeAttrs.

  misc.nix still contains a lot of stuff that should be refactored and
  moved to other files.

svn path=/nixpkgs/trunk/; revision=14013

pkgs/lib/attrsets.nix

@@ -0,0 +1,22 @@
+# Operations on attribute sets.
+
+with { inherit (builtins) head tail; };
+
+rec {
+  inherit (builtins) attrNames listToAttrs hasAttr isAttrs;
+
+
+  # Return an attribute from nested attribute sets.  For instance ["x"
+  # "y"] applied to some set e returns e.x.y, if it exists.  The
+  # default value is returned otherwise.  !!! there is also
+  # builtins.getAttr (is there a better name for this function?)
+  getAttr = attrPath: default: e:
+    let attr = head attrPath;
+    in
+      if attrPath == [] then e
+      else if builtins ? hasAttr && hasAttr attr e
+      then getAttr (tail attrPath) default (builtins.getAttr attr e)
+      else default;
+
+
+}