diff --git a/CHANGELOG.md b/CHANGELOG.md
index 10e01a6dcbc6b62b04fff3ca7909b07fcbb2d2af..425d8406dfcd36aa40a16f133652ad192c194393 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,8 @@
 # Changelog for the repository
 
+## 2020-09-03
+- Updated ast with Display
+
 ## 2020-09-03
 - Added src/comment 
     - single and multiline comments
diff --git a/src/ast/ast.rs b/src/ast/ast.rs
index e79e70de9cab432b6a84b5ac4e10179b50c3db3e..50417318082330ea12b8623d3d2fb7ee57daa764 100644
--- a/src/ast/ast.rs
+++ b/src/ast/ast.rs
@@ -1,7 +1,22 @@
+use std::fmt;
+
 // ast
 
-#[derive(Debug)]
+// println!("{:?}", ..)
+#[derive(Debug)] 
 pub enum NumOrId {
     Num(usize),
     Id(String),
+}
+
+// println!("{}", ..)
+impl fmt::Display for NumOrId {
+
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            NumOrId::Num(i) => write!(f, "{}", i)?,
+            NumOrId::Id(s) => write!(f, "{}", s)?,
+        };
+        Ok(())
+    }
 }
\ No newline at end of file
diff --git a/src/ast/main.rs b/src/ast/main.rs
index 2a0f6624d6b3f24a0f215bee20eee2f062967803..998eed7d08991ba6c56c49d8c78aa26c190709c8 100644
--- a/src/ast/main.rs
+++ b/src/ast/main.rs
@@ -10,10 +10,13 @@ fn main() {
     println!("minimal");
     println!("{:?}", NumOrIdParser::new().parse("123"));
     println!("{:?}", NumOrIdParser::new().parse("a1_a"));
+
+    println!("{}", NumOrIdParser::new().parse("123").unwrap());
+    println!("{}", NumOrIdParser::new().parse("a1_a").unwrap());
 }
 
 #[test]
 fn parse_num_or_id() {
-    // println!("{:?}", NumOrIdParser::new().parse("123"));
-    // println!("{:?}", NumOrIdParser::new().parse("a1_a"));
+   assert_eq!(format!("{}", NumOrIdParser::new().parse("123").unwrap()), "123");
+   assert_eq!(format!("{}", NumOrIdParser::new().parse("a1_a").unwrap()), "a1_a");
 }
diff --git a/src/ast/parser.lalrpop b/src/ast/parser.lalrpop
index d749efaba2644b25cd0beced5b5b05d3a66e21e5..87f0b32f26126cf26e612b5fc40cdda48d17a881 100644
--- a/src/ast/parser.lalrpop
+++ b/src/ast/parser.lalrpop
@@ -4,7 +4,7 @@ use crate::ast::*;
 
 grammar;
 
-pub NumOrId : NumOrId = {
+pub NumOrId: NumOrId = {
     Num => NumOrId::Num(<>),
     Id => NumOrId::Id(<>),
 }