From 74dbf724a51a0eab3e4c10560df3281beec51b92 Mon Sep 17 00:00:00 2001
From: Daniel M <daniel.q.mueller@stud.h-da.de>
Date: Fri, 28 Jan 2022 14:11:39 +0100
Subject: [PATCH] Implement parentheses grouping

---
 src/lexer.rs  |  8 ++++++++
 src/parser.rs | 15 ++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/lexer.rs b/src/lexer.rs
index 62860b6..fbd8ab5 100644
--- a/src/lexer.rs
+++ b/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),
diff --git a/src/parser.rs b/src/parser.rs
index 30c0cea..1813719 100644
--- a/src/parser.rs
+++ b/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),
         }
     }