```
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)
```
#include "UserDefinedSQLFunctionVisitor.h"
#include <unordered_map>
#include <stack>
#include <Parsers/ASTFunction.h>
#include <Parsers/ASTCreateFunctionQuery.h>
#include <Parsers/ASTExpressionList.h>
#include <Parsers/ASTIdentifier.h>
#include <Interpreters/UserDefinedSQLFunctionFactory.h>
namespace DB
{
namespace ErrorCodes
{
    extern const int UNSUPPORTED_METHOD;
}
void UserDefinedSQLFunctionMatcher::visit(ASTPtr & ast, Data &)
{
    auto * function = ast->as<ASTFunction>();
    if (!function)
        return;
    auto result = tryToReplaceFunction(*function);
    if (result)
        ast = result;
}
bool UserDefinedSQLFunctionMatcher::needChildVisit(const ASTPtr &, const ASTPtr &)