diff --git a/src/expr.rs b/src/expr.rs
new file mode 100644
index 0000000..47143b9
--- /dev/null
+++ b/src/expr.rs
@@ -0,0 +1,30 @@
+use crate::token::Token;
+
+pub struct Binary {
+    left: Expr,
+    operator: Token,
+    right: Expr,
+}
+
+pub struct Grouping {
+    expression: Expr,
+}
+
+pub enum Literal {
+    LiteralNumber(i8),
+    LiteralString(String),
+    LiteralBool(bool),
+    LiteralNil,
+}
+
+pub struct Unary {
+    operator: Token,
+    right: Expr,
+}
+
+pub enum Expr {
+    Binary ,
+    Grouping,
+    Literal,
+    Unary,
+}
diff --git a/src/main.rs b/src/main.rs
index e5843a4..398de11 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -6,6 +6,7 @@ mod rlox_interpreter;
 mod scanner;
 mod token;
 mod token_type;
+mod expr;
 
 use crate::rlox_interpreter::RLoxInterpreter;
 
@@ -34,4 +35,4 @@ fn main() {
 // https://github.com/munificent/craftinginterpreters/wiki/Lox-implementations#rust
 
 // Pause :
-// http://www.craftinginterpreters.com/scanning.html#lexical-errors
+// http://www.craftinginterpreters.com/representing-code.html#working-with-trees