diff --git a/rlox/src/main.rs b/rlox/src/main.rs
index a65eff0..c71c35a 100644
--- a/rlox/src/main.rs
+++ b/rlox/src/main.rs
@@ -2,6 +2,8 @@ mod vm;
 
 fn main() {
     let mut chunk = vm::Chunk::new("TEST".to_string());
-    chunk.add(vm::Op::Return);
+    chunk.add_op(vm::Op::Return, 1);
+    chunk.add_op(vm::Op::Constant { offset: 0 }, 1);
+    chunk.add_constant(vm::Value::from(3.14));
     println!("{:?}", chunk);
 }
diff --git a/rlox/src/vm.rs b/rlox/src/vm.rs
index 1715a2a..535e75c 100644
--- a/rlox/src/vm.rs
+++ b/rlox/src/vm.rs
@@ -1,34 +1,73 @@
+use std::convert::From;
 use std::fmt;
 
 #[repr(u8)]
-#[derive(Debug)]
+#[derive(Copy, Clone, Debug)]
 pub enum Op {
-    Return
+    Return,
+    Constant { offset: usize },
+}
+
+#[derive(Debug)]
+pub struct Value {
+    val: f64,
+}
+
+impl From<f64> for Value {
+    fn from(value: f64) -> Self {
+        Value { val: value }
+    }
 }
 
 pub struct Chunk {
     code: Vec<Op>,
-    name: String
+    name: String,
+    debug_info: Vec<usize>,
+    constants: Vec<Value>,
 }
 
 impl Chunk {
-    pub fn new(name: String) -> Chunk {
+    pub fn new(name: String) -> Self {
         Chunk {
             code: Vec::new(),
-            name
+            name: name,
+            debug_info: Vec::new(),
+            constants: Vec::new(),
         }
     }
 
-    pub fn add(&mut self, op: Op) {
-        self.code.push(op)
+    pub fn add_op(&mut self, op: Op, line: usize) {
+        self.code.push(op);
+        self.debug_info.push(line);
+
+    }
+
+    pub fn add_constant(&mut self, value: Value) {
+        self.constants.push(value);
     }
 }
 
 impl fmt::Debug for Chunk {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
         writeln!(f, "-*-*- {} -*-*-", self.name)?;
-        for (idx, op) in self.code.iter().enumerate() {
-            write!(f, "{:04}  {:?}", idx, op)?;
+        for (idx, op) in self.code.iter().copied().enumerate() {
+            write!(f, "{:04}  ", idx)?;
+
+            let line = self.debug_info[idx];
+
+            if idx > 0 && self.debug_info[idx-1] == line {
+                write!(f, "   |  ")?;
+            } else {
+                write!(f, "{:4}  ", line)?;
+            }
+
+            match op {
+                Op::Return => writeln!(f, "{:?}", op),
+                Op::Constant { offset } =>
+                    f.debug_struct("Constant")
+                     .field("val", &self.constants[offset].val)
+                     .finish(),
+            }?;
         }
 
         return Ok(());