```
2021.10.22 07:14:33.963099 [ 3451059 ] {} <Error> Application: DB::Exception: Syntax error (in file ./user_defined/function_a_function.sql): failed at position 39 ('->'): -> ch(2)

$ cat ./user_defined/function_a_function.sql
CREATE FUNCTION a_function AS tuple() -> ch(2)
```
{
    return "Function" + (delim + name);
}
ASTPtr ASTFunction::clone() const
{
    auto res = std::make_shared<ASTFunction>(*this);
    res->children.clear();
    if (arguments) { res->arguments = arguments->clone(); res->children.push_back(res->arguments); }
    if (parameters) { res->parameters = parameters->clone(); res->children.push_back(res->parameters); }
    if (window_definition)
    {
        res->window_definition = window_definition->clone();
        res->children.push_back(res->window_definition);
    }
    return res;
}
void ASTFunction::updateTreeHashImpl(SipHash & hash_state) const
{
    hash_state.update(name.size());
    hash_state.update(name);
    IAST::updateTreeHashImpl(hash_state);
}
ASTPtr ASTFunction::toLiteral() const