* Export the nix-env derivation name parsing and version comparison

logic through the `parseDrvName' and `compareVersions' primops.
  This will allow expressions to easily check whether some dependency
  is a specific needed version or falls in some version range.  See
  tests/lang/eval-okay-versions.nix for examples.

src/libexpr/names.hh

@@ -0,0 +1,33 @@
+#ifndef __NAMES_H
+#define __NAMES_H
+
+#include "types.hh"
+
+
+namespace nix {
+
+
+struct DrvName
+{
+    string fullName;
+    string name;
+    string version;
+    unsigned int hits;
+
+    DrvName();
+    DrvName(const string & s);
+    bool matches(DrvName & n);
+};
+
+
+typedef list<DrvName> DrvNames;
+
+
+int compareVersions(const string & v1, const string & v2);
+DrvNames drvNamesFromArgs(const Strings & opArgs);
+
+
+}
+
+
+#endif /* !__NAMES_H */