* Big cleanup of the semantics of paths, strings, contexts, string

concatenation and string coercion.  This was a big mess (see
  e.g. NIX-67).  Contexts are now folded into strings, so that they
  don't cause evaluation errors when they're not expected.  The
  semantics of paths has been clarified (see nixexpr-ast.def).
  toString() and coerceToString() have been merged.

  Semantic change: paths are now copied to the store when they're in a
  concatenation (and in most other situations - that's the
  formalisation of the meaning of a path).  So

    "foo " + ./bla

  evaluates to "foo /nix/store/hash...-bla", not "foo
  /path/to/current-dir/bla".  This prevents accidental impurities, and
  is more consistent with the treatment of derivation outputs, e.g.,
  `"foo " + bla' where `bla' is a derivation.  (Here `bla' would be
  replaced by the output path of `bla'.)

src/libutil/aterm.cc

@@ -41,3 +41,13 @@ ATerm nix::toATerm(const string & s)
 {
     return toATerm(s.c_str());
 }
+
+
+ATermList nix::toATermList(const StringSet & ss)
+{
+    ATermList l = ATempty;
+    for (StringSet::const_reverse_iterator i = ss.rbegin();
+         i != ss.rend(); ++i)
+        l = ATinsert(l, toATerm(*i));
+    return l;
+}

src/libutil/aterm.hh

@@ -43,6 +43,7 @@ Error badTerm(const format & f, ATerm t);
 ATerm toATerm(const char * s);
 ATerm toATerm(const string & s);
 
+ATermList toATermList(const StringSet & ss);
  
 }