const tensorflow::GraphDef& graph_def) {
  std::vector<std::pair<string, string>> grads;
  for (const tensorflow::GradientDef& grad : graph_def.library().gradient()) {
    grads.emplace_back(grad.function_name(), grad.gradient_func());
  }
  std::sort(grads.begin(), grads.end());
  return grads;
}

std::vector<string> GetFuncNames(const tensorflow::GraphDef& graph_def) {
  std::vector<string> names;

	// Used during evaluation for aggregation funcs
	aggregate *aggVal
}

// SimpleArgFunc represents functions with simple expression
// arguments.
type SimpleArgFunc struct {
	FunctionName string `parser:" @(\"AVG\" | \"MAX\" | \"MIN\" | \"SUM\" |  \"COALESCE\" | \"NULLIF\" | \"TO_STRING\" | \"TO_TIMESTAMP\" | \"UTCNOW\" | \"CHAR_LENGTH\" | \"CHARACTER_LENGTH\" | \"LOWER\" | \"UPPER\") "`

	errNonTimestampArg   = errors.New("Expected a timestamp argument")
)

func (e *FuncExpr) getFunctionName() FuncName {
	switch {
	case e.SFunc != nil:
		return FuncName(strings.ToUpper(e.SFunc.FunctionName))
	case e.Count != nil:
		return aggFnCount
	case e.Cast != nil:
		return sqlFnCast
	case e.Substring != nil:
		return sqlFnSubstring
	case e.Extract != nil:
		return sqlFnExtract
	case e.Trim != nil: