diff --git a/src/builtin_function/assign.rs b/src/builtin_function/assign.rs
index 0b049cd..cb7d5c0 100644
--- a/src/builtin_function/assign.rs
+++ b/src/builtin_function/assign.rs
@@ -34,7 +34,7 @@ mod tests {
 
     #[test]
     fn assign_value_and_variable() {
-        let mut runtime = Runtime::new(|_| {}, || "".to_string());
+        let mut runtime = Runtime::new(Box::new(|_| {}), Box::new(|| "".to_string()));
 
         assign(
             &mut runtime,
diff --git a/src/builtin_function/control_flow/new_tag.rs b/src/builtin_function/control_flow/new_tag.rs
index 31ebd02..9bac30d 100644
--- a/src/builtin_function/control_flow/new_tag.rs
+++ b/src/builtin_function/control_flow/new_tag.rs
@@ -28,7 +28,7 @@ mod tests {
 
     #[test]
     fn new_tag_test() {
-        let mut runtime = Runtime::new(|_| {}, || "".to_string());
+        let mut runtime = Runtime::new(Box::new(|_| {}), Box::new(|| "".to_string()));
 
         new_tag(
             &mut runtime,
diff --git a/src/builtin_function/debugger/dump.rs b/src/builtin_function/debugger/dump.rs
index 6dacc35..49d9493 100644
--- a/src/builtin_function/debugger/dump.rs
+++ b/src/builtin_function/debugger/dump.rs
@@ -4,13 +4,22 @@ use crate::{
 };
 
 pub fn dump(runtime: &mut Runtime, executable: &ExecutableLine) -> Result<()> {
-    runtime.std_out(format!("------- Memory dump line: {}", executable.line_number).as_str());
+    let mut result = String::new();
     for variable in runtime.variables.iter() {
         let name = variable.0;
         let value = variable.1;
-        runtime.std_out(format!("{} -> ${}", value.to_string(), name).as_str())
+        result.push_str(format!("{} -> ${}\n", value.to_string(), name).as_str())
     }
-    runtime.std_out("------- Memory dump ends");
+    result.pop();
+    runtime.std_out(
+        format!(
+            "------- Memory dump line: {} -------",
+            executable.line_number
+        )
+        .as_str(),
+    );
+    runtime.std_out(&result);
+    runtime.std_out("------- Memory dump ends -------");
 
     Ok(())
 }
diff --git a/src/builtin_function/std_io/input.rs b/src/builtin_function/std_io/input.rs
index 265d7cf..fa0aa74 100644
--- a/src/builtin_function/std_io/input.rs
+++ b/src/builtin_function/std_io/input.rs
@@ -1,6 +1,6 @@
+use crate::builtin_function::utils::returns;
 use crate::common::data_type::DataType;
 use crate::common::errors::Result;
-use crate::builtin_function::utils::returns;
 use crate::{common::executable::ExecutableLine, runtime::Runtime};
 
 pub fn input(runtime: &mut Runtime, executable: &ExecutableLine) -> Result<()> {
@@ -19,7 +19,7 @@ mod tests {
 
     #[test]
     fn input_test() {
-        let mut runtime = Runtime::new(|_| {}, || "test".to_string());
+        let mut runtime = Runtime::new(Box::new(|_| {}), Box::new(|| "test".to_string()));
 
         input(
             &mut runtime,
diff --git a/src/builtin_function/std_io/println.rs b/src/builtin_function/std_io/println.rs
index 75635ba..81be322 100644
--- a/src/builtin_function/std_io/println.rs
+++ b/src/builtin_function/std_io/println.rs
@@ -1,5 +1,5 @@
-use crate::common::errors::Result;
 use crate::builtin_function::utils::param_to_datatype;
+use crate::common::errors::Result;
 use crate::{common::executable::ExecutableLine, runtime::Runtime};
 
 pub fn println(runtime: &mut Runtime, executable: &ExecutableLine) -> Result<()> {
@@ -23,10 +23,10 @@ mod tests {
     #[test]
     fn print_string() {
         let mut runtime = Runtime::new(
-            |x| {
+            Box::new(|x| {
                 assert_eq!(x, "test");
-            },
-            || "".to_string(),
+            }),
+            Box::new(|| "".to_string()),
         );
 
         println(
@@ -44,10 +44,10 @@ mod tests {
     #[test]
     fn print_int() {
         let mut runtime = Runtime::new(
-            |x| {
+            Box::new(|x| {
                 assert_eq!(x, "2");
-            },
-            || "".to_string(),
+            }),
+            Box::new(|| "".to_string()),
         );
 
         println(
@@ -65,10 +65,10 @@ mod tests {
     #[test]
     fn print_many() {
         let mut runtime = Runtime::new(
-            |x| {
+            Box::new(|x| {
                 assert_eq!(x, "2, false");
-            },
-            || "".to_string(),
+            }),
+            Box::new(|| "".to_string()),
         );
 
         println(
diff --git a/src/runners/eval.rs b/src/runners/eval.rs
index 8ad010e..f2ac05c 100644
--- a/src/runners/eval.rs
+++ b/src/runners/eval.rs
@@ -4,7 +4,12 @@ use crate::compile::parser::Parser;
 use crate::compile::preprocessor::Preprocessor;
 use crate::runtime::Runtime;
 
-pub fn eval(code: String, std_out: fn(&str), std_in: fn() -> String, on_error: fn(ChapError)) {
+pub fn eval<'a>(
+    code: String,
+    std_out: Box<dyn FnMut(&str) + 'a>,
+    std_in: Box<dyn FnMut() -> String + 'a>,
+    mut on_error: impl FnMut(ChapError),
+) {
     let mut runtime = match make_runtime(code, std_out, std_in) {
         Ok(rt) => rt,
         Err(e) => {
@@ -30,7 +35,11 @@ pub fn eval(code: String, std_out: fn(&str), std_in: fn() -> String, on_error: f
     }
 }
 
-fn make_runtime(code: String, std_out: fn(&str), std_in: fn() -> String) -> Result<Runtime> {
+fn make_runtime<'a>(
+    code: String,
+    std_out: Box<dyn FnMut(&str) + 'a>,
+    std_in: Box<dyn FnMut() -> String + 'a>,
+) -> Result<Runtime<'a>> {
     let mut preprocessor = Preprocessor::default();
     let mut parser = Parser::default();
     let mut runtime = Runtime::new(std_out, std_in);
@@ -51,10 +60,54 @@ fn make_runtime(code: String, std_out: fn(&str), std_in: fn() -> String) -> Resu
 
 #[cfg(test)]
 mod tests {
+    use crate::common::errors::ChapError;
+
     use super::eval;
 
     #[test]
     fn test_eval() {
-        eval("3".to_string(), |_| {}, || "".to_string(), |_| {});
+        eval(
+            "3".to_string(),
+            Box::new(|_| {}),
+            Box::new(|| "".to_string()),
+            |_| {},
+        );
+    }
+
+    #[test]
+    fn test_eval_closure() {
+        let input = "INPUT".to_string();
+        let mut output = "".to_string();
+
+        eval(
+            "input -> $a; $a -> print".to_string(),
+            Box::new(|out| {
+                output = out.to_string();
+            }),
+            Box::new(|| {
+                return input.clone();
+            }),
+            |_| {},
+        );
+        assert_eq!(input, output);
+    }
+
+    #[test]
+    fn test_eval_error() {
+        let mut error: Option<ChapError> = None;
+        eval(
+            "a".to_string(),
+            Box::new(|_| {}),
+            Box::new(|| {
+                return "".to_string();
+            }),
+            |e| {
+                error = Some(e);
+            },
+        );
+
+        if let None = error {
+            assert!(false, "error not happened");
+        }
     }
 }
diff --git a/src/runners/file_executor.rs b/src/runners/file_executor.rs
index be7a78a..4adafde 100644
--- a/src/runners/file_executor.rs
+++ b/src/runners/file_executor.rs
@@ -7,16 +7,16 @@ pub fn file_executor(file_name: &str) {
     let code = read_to_string(file_name).unwrap();
     eval(
         code,
-        |msg| {
+        Box::new(|msg| {
             println!("{}", msg);
-        },
-        || {
+        }),
+        Box::new(|| {
             let mut buffer = String::new();
             let stdin = io::stdin(); // We get `Stdin` here.
             stdin.read_line(&mut buffer).unwrap();
             buffer = buffer.replace('\n', "").trim().to_string();
             buffer
-        },
+        }),
         |e| {
             e.exit_with_error();
         },
diff --git a/src/runners/repl.rs b/src/runners/repl.rs
index 792a629..da5613a 100644
--- a/src/runners/repl.rs
+++ b/src/runners/repl.rs
@@ -16,10 +16,10 @@ pub fn start_repl() {
     let mut reader = DefaultEditor::new().unwrap(); // TODO: handle error
 
     let mut runtime = Runtime::new(
-        |msg| {
+        Box::new(|msg| {
             println!("{}", msg);
-        },
-        || String::from(""),
+        }),
+        Box::new(|| String::from("")),
     );
 
     loop {
diff --git a/src/runtime.rs b/src/runtime.rs
index 5dfb6de..bbc159b 100644
--- a/src/runtime.rs
+++ b/src/runtime.rs
@@ -3,17 +3,20 @@ use crate::common::errors::Result;
 use crate::common::executable::ExecutableLine;
 use std::collections::HashMap;
 
-pub struct Runtime {
+pub struct Runtime<'a> {
     pub executables: Vec<ExecutableLine>,
     pub variables: HashMap<String, DataType>, // <variable name, variable value>
     pub tags: HashMap<String, usize>,         // <tag name, index in executables vector>
     pub current_line: usize,
-    pub std_out: fn(&str),
-    pub std_in: fn() -> String,
+    pub std_out: Box<dyn FnMut(&str) + 'a>,
+    pub std_in: Box<dyn FnMut() -> String + 'a>,
 }
 
-impl Runtime {
-    pub fn new(std_out: fn(&str), std_in: fn() -> String) -> Self {
+impl<'a> Runtime<'a> {
+    pub fn new(
+        std_out: Box<dyn FnMut(&str) + 'a>,
+        std_in: Box<dyn FnMut() -> String + 'a>,
+    ) -> Self {
         Self {
             executables: vec![],
             variables: HashMap::new(),
@@ -43,11 +46,11 @@ impl Runtime {
         Ok(())
     }
 
-    pub fn std_out(&self, msg: &str) {
+    pub fn std_out(&mut self, msg: &str) {
         (self.std_out)(msg);
     }
 
-    pub fn std_in(&self) -> String {
+    pub fn std_in(&mut self) -> String {
         (self.std_in)()
     }
 }
@@ -61,7 +64,7 @@ mod tests {
 
     #[test]
     fn simple_execution_test() {
-        let mut rt = Runtime::new(|_| {}, || "".to_string());
+        let mut rt = Runtime::new(Box::new(|_| {}), Box::new(|| "".to_string()));
 
         assert_eq!(rt.current_line, 0);
         rt.on_new_line(ExecutableLine::new(
@@ -82,10 +85,10 @@ mod tests {
     #[test]
     fn runtime_std_test() {
         let mut rt = Runtime::new(
-            |x| {
+            Box::new(|x| {
                 assert_eq!(x, "the text");
-            },
-            || "the text".to_string(),
+            }),
+            Box::new(|| "the text".to_string()),
         );
 
         rt.on_new_line(ExecutableLine::new(