added the null literal

src/ast.rs

@@ -5,6 +5,7 @@ pub trait Expr: Stmt {}
 pub enum NodeType {
     Program(Program),
     NumericLiteral(NumericLiteral),
+    NullLiteral(NullLiteral),
     Identifier(Identifier),
     BinaryExpr(BinaryExpr),
     EOF,
@@ -32,6 +33,9 @@ pub struct NumericLiteral {
     pub value: f64,
 }
 
+#[derive(Debug)]
+pub struct NullLiteral {}
+
 impl Stmt for Program {}
 
 impl Stmt for NumericLiteral {}

src/lexer.rs

@@ -21,18 +21,20 @@ pub mod interpreter {
 
     #[derive(Clone)]
     pub enum Token {
-        Number(String),
-        Identifier(String),
-        Equals,
-        Let,
-        OpenParen,
-        CloseParen,
         BinaryOperator(String),
+        Identifier(String),
+        Number(String),
+        CloseParen,
+        OpenParen,
+        Equals,
+        Null,
+        Let,
         EOF,
     }
 
     static KEYWORDS: phf::Map<&'static str, Token> = phf::phf_map! {
         "let" => Token::Let,
+        "null" => Token::Null,
     };
 
     impl Token {
@@ -79,6 +81,7 @@ pub mod interpreter {
                 Token::OpenParen => write!(f, "Token::OpenParen"),
                 Token::CloseParen => write!(f, "Token::CloseParen"),
                 Token::EOF => write!(f, "Token::EOF"),
+                Token::Null => write!(f, "Token::Null"),
             }
         }
     }

src/parser.rs

@@ -1,6 +1,6 @@
 use std::process;
 
-use crate::ast::{BinaryExpr, Identifier, NodeType, NumericLiteral, Program};
+use crate::ast::{BinaryExpr, Identifier, NodeType, NullLiteral, NumericLiteral, Program};
 use crate::lexer::interpreter;
 
 pub struct Parser {
@@ -50,6 +50,7 @@ impl Parser {
             Token::Number(n) => NodeType::NumericLiteral(NumericLiteral {
                 value: n.parse().expect(&format!("Failed to parse number: {}", n)),
             }),
+            Token::Null => NodeType::NullLiteral(NullLiteral {}),
             Token::EOF => NodeType::EOF,
 
             Token::OpenParen => {