lib: add versions library

lib/default.nix

@@ -24,7 +24,7 @@ let
     maintainers = callLibs ./maintainers.nix;
     meta = callLibs ./meta.nix;
     sources = callLibs ./sources.nix;
-
+    versions = callLibs ./versions.nix;
 
     # module system
     modules = callLibs ./modules.nix;

lib/versions.nix

@@ -0,0 +1,47 @@
+/* Version string functions. */
+{ lib }:
+
+let
+
+  splitVersion = builtins.splitVersion or (lib.splitString ".");
+
+in
+
+rec {
+
+  /* Get the major version string from a string.
+
+    Example:
+      major "1.2.3"
+      => "1"
+  */
+  major = v: builtins.elemAt (splitVersion v) 0;
+
+  /* Get the minor version string from a string.
+
+    Example:
+      minor "1.2.3"
+      => "2"
+  */
+  minor = v: builtins.elemAt (splitVersion v) 1;
+
+  /* Get the patch version string from a string.
+
+    Example:
+      patch "1.2.3"
+      => "3"
+  */
+  patch = v: builtins.elemAt (splitVersion v) 2;
+
+  /* Get string of the first two parts (major and minor)
+     of a version string.
+
+     Example:
+       majorMinor "1.2.3"
+       => "1.2"
+  */
+  majorMinor = v:
+    builtins.concatStringsSep "."
+    (lib.take 2 (splitVersion v));
+
+}