add error handling for unterminated strings

src/errors.rs

@@ -2,6 +2,7 @@ use thiserror::Error;
 
 use crate::frontend::{ast::Expr, lexer::Token};
 
+// Universal Errors used by functions like parser::produce_ast()
 #[derive(Error, Debug)]
 pub enum Error {
     #[error("Lexer Error: {0}")]
@@ -17,6 +18,7 @@ pub enum Error {
     // TODO: RuntimeError(RuntimeError),
 }
 
+// Lexer-specific Errors
 #[derive(Error, Debug)]
 pub enum LexerError {
     #[error("Unrecognized character '{0}'")]
@@ -35,6 +37,7 @@ pub enum LexerError {
     InternalError(String),
 }
 
+// Parser-specific Errors
 #[derive(Error, Debug)]
 pub enum ParserError {
     #[error("Lexer Error: {0}")]

src/frontend/lexer.rs

@@ -408,7 +408,8 @@ fn tokenize_string_literal(
         match ch {
             '"' => {
                 chars.next(); // Consume the closing quote
-                break;
+                tokens.push(Token::StringLiteral(literal));
+                return Ok(());
             }
             '\\' => {
                 chars.next(); // Consume the backslash
@@ -430,6 +431,5 @@ fn tokenize_string_literal(
             }
         }
     }
-    tokens.push(Token::StringLiteral(literal));
-    Ok(())
+    Err(LexerError::UnterminatedStringLiteral)
 }