message: Created a new type: udf_function_t, and added it as a class member and initialized in the constructors.
diff: #include "duckdb/execution/expression_executor_state.hpp"
  #include "duckdb/function/function.hpp"
  +#include <iostream>
  +using namespace std;
  +
  namespace duckdb {
  class BoundFunctionExpression;
  class ScalarFunctionCatalogEntry;
  @@ -26,19 +29,22 @@ typedef unique_ptr<FunctionData> (*bind_scalar_function_t)(BoundFunctionExpressi
  //! Adds the dependencies of this BoundFunctionExpression to the set of dependencies
  typedef void (*dependency_function_t)(BoundFunctionExpression &expr, unordered_set<CatalogEntry *> &dependencies);
  +//! The type of UDF functions
  +typedef std::function<void(DataChunk &, ExpressionState &, Vector &)> udf_function_t;
  +
  class ScalarFunction : public SimpleFunction {
  public:
  ScalarFunction(string name, vector<SQLType> arguments, SQLType return_type, scalar_function_t function,
  bool has_side_effects = false, bind_scalar_function_t bind = nullptr,
  - dependency_function_t dependency = nullptr)
  + dependency_function_t dependency = nullptr, udf_function_t udf_function = nullptr)
  : SimpleFunction(name, arguments, return_type, has_side_effects), function(function), bind(bind),
  - dependency(dependency) {
  + dependency(dependency), udf_function(udf_function) {
  }
  ScalarFunction(vector<SQLType> arguments, SQLType return_type, scalar_function_t function,
  bool has_side_effects = false, bind_scalar_function_t bind = nullptr,
  - dependency_function_t dependency = nullptr)
  - : ScalarFunction(string(), arguments, return_type, function, has_side_effects, bind, dependency) {
  + dependency_function_t dependency = nullptr, udf_function_t udf_function = nullptr)
  + : ScalarFunction(string(), arguments, return_type, function, has_side_effects, bind, dependency, udf_function) {
  }
  //! The main scalar function to execute
  @@ -48,6 +54,9 @@ public:
  // The dependency function (if any)
  dependency_function_t dependency;
  + //! An UDF function to execute
  + udf_function_t udf_function;
  +
  static unique_ptr<BoundFunctionExpression> BindScalarFunction(ClientContext &context, string schema, string name,
  vector<SQLType> &arguments,
  vector<unique_ptr<Expression>> children,
  