Helper method that expands a dotted string into MemberExpression
@param str
@returns {*}
function expandMemberExpression(str) {
  var segs = str.split(".");
  var expr = types.memberExpression(types.identifier(segs[0]), types.identifier(segs[1]));
  for (var i = 2; i < segs.length; i++) {
    expr = types.memberExpression(expr, types.identifier(segs[i]));
  }
  return expr;
}