addFunctionsDefinedInScript doc

Author: DQinYuan

README-EN-source.adoc

@@ -141,6 +141,15 @@ include::./src/test/java/com/alibaba/qlexpress4/test/function/HelloFunction.java
 include::./src/test/java/com/alibaba/qlexpress4/Express4RunnerTest.java[tag=customComplexFunction]
 ----
 
+QLExpress4 also supports adding custom functions through QLExpress scripts. Note that variables defined outside of functions (such as defineTime in the example) are initialized when the function is defined and will not be recalculated when the function is subsequently called.
+
+[source,java,indent=0]
+----
+include::./src/test/java/com/alibaba/qlexpress4/Express4RunnerTest.java[tag=addFunctionsDefinedInScript]
+----
+
+It is recommended to use Java to define custom functions as much as possible, as this can provide better performance and stability.
+
 === Validating Syntax Correctness
 
 To validate syntax correctness without executing scripts: call `parseToSyntaxTree` and catch exceptions. If `QLSyntaxException` is caught, it indicates syntax errors exist.

README-source.adoc

@@ -143,6 +143,15 @@ include::./src/test/java/com/alibaba/qlexpress4/test/function/HelloFunction.java
 include::./src/test/java/com/alibaba/qlexpress4/Express4RunnerTest.java[tag=customComplexFunction]
 ----
 
+QLExpress4还支持通过QLExpress脚本添加自定义函数。需要注意的是，在函数外定义的变量（如示例中的defineTime）在函数定义时就已初始化完成，后续调用函数时不会重新计算该变量的值。
+
+[source,java,indent=0]
+----
+include::./src/test/java/com/alibaba/qlexpress4/Express4RunnerTest.java[tag=addFunctionsDefinedInScript]
+----
+
+建议尽可能使用Java方式定义自定义函数，这样可以获得更好的性能和稳定性。
+
 === 校验语法正确性
 
 在不执行脚本的情况下，单纯校验语法的正确性: 调用 `parseToSyntaxTree` 并且捕获异常，如果捕获到 `QLSyntaxException`，则说明存在语法错误