Implement parentheses grouping

src/lexer.rs

@@ -7,6 +7,12 @@ pub enum Token {
     /// Integer literal (64-bit)
     I64(i64),
 
+    /// Left parenthesis ('(')
+    LParen,
+
+    /// Right parentheses (')')
+    RParen,
+
     /// Plus (+)
     Add,
 
@@ -99,6 +105,8 @@ impl<'a> Lexer<'a> {
                 '|' => tokens.push(Token::BOr),
                 '&' => tokens.push(Token::BAnd),
                 '^' => tokens.push(Token::BXor),
+                '(' => tokens.push(Token::LParen),
+                ')' => tokens.push(Token::RParen),
 
                 //TODO: Don't panic, keep calm
                 _ => panic!("Lexer encountered unexpected char: '{}'", ch),

src/parser.rs

@@ -47,7 +47,7 @@ pub enum Ast {
 /*
 ## Grammar
 ### Expressions
-expr_primary = LITERAL
+expr_primary = LITERAL | "(" expr ")"
 expr_mul = expr_primary (("*" | "/" | "%") expr_primary)*
 expr_add = expr_mul (("+" | "-") expr_mul)*
 expr_shift = expr_add ((">>" | "<<") expr_add)*
@@ -110,6 +110,19 @@ impl<T: Iterator<Item = Token>> Parser<T> {
         match self.next() {
             Token::I64(val) => Ast::I64(val),
 
+            Token::LParen => {
+                // The tokens was an opening parenthesis, so parse a full expression again as the 
+                // expression inside the parentheses `"(" expr ")"`
+                let inner = self.parse_expr();
+
+                // If there is no closing parenthesis after the expression, it is a syntax error
+                if !matches!(self.next(), Token::RParen) {
+                    panic!("Error parsing primary expr: Missing closing parenthesis ')'");
+                }
+
+                inner
+            }
+
             tok => panic!("Error parsing primary expr: Unexpected Token '{:?}'", tok),
         }
     }