feat: 添加对单引号字符串的支持，更新词法分析器和相关测试用例

src/interpreter/interpreter.rs

@@ -750,6 +750,30 @@ mod tests {
         }
     }
 
+    #[test]
+    fn eval_single_quoted_string() {
+        match eval_expr("'hello'") {
+            Value::String(s) => assert_eq!(s, "hello"),
+            v => panic!("Expected String, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn eval_mixed_quotes_concat() {
+        match eval_expr("\"a\" + 'b'") {
+            Value::String(s) => assert_eq!(s, "ab"),
+            v => panic!("Expected String, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn eval_single_quote_containing_double() {
+        match eval_expr("'he\"llo'") {
+            Value::String(s) => assert_eq!(s, "he\"llo"),
+            v => panic!("Expected String, got {:?}", v),
+        }
+    }
+
     #[test]
     fn eval_string_plus_number() {
         match eval_expr("\"a\" + 42") {

src/lexer/lexer.rs

@@ -157,7 +157,7 @@ impl Lexer {
                 }
             }
 
-            '"' => return self.string_literal(line, column, errors),
+            '"' | '\'' => return self.string_literal(line, column, errors, c),
 
             c if c.is_ascii_digit() => {
                 return Some(self.number_literal(c, line, column));
@@ -230,10 +230,11 @@ impl Lexer {
         line: usize,
         column: usize,
         errors: &mut Vec<RuntimeError>,
+        quote: char,
     ) -> Option<Token> {
         let mut value = String::new();
 
-        while !self.is_at_end() && self.peek() != '"' {
+        while !self.is_at_end() && self.peek() != quote {
             let c = self.advance();
             if c == '\\' {
                 // Handle escape sequences
@@ -246,6 +247,7 @@ impl Lexer {
                     't' => value.push('\t'),
                     'r' => value.push('\r'),
                     '"' => value.push('"'),
+                    '\'' => value.push('\''),
                     '\\' => value.push('\\'),
                     other => {
                         errors.push(RuntimeError::lex(
@@ -254,11 +256,11 @@ impl Lexer {
                             column,
                         ));
                         // Consume the rest of the string to avoid cascading errors
-                        while !self.is_at_end() && self.peek() != '"' {
+                        while !self.is_at_end() && self.peek() != quote {
                             self.advance();
                         }
                         if !self.is_at_end() {
-                            self.advance(); // consume closing "
+                            self.advance(); // consume closing quote
                         }
                         return None;
                     }
@@ -273,7 +275,7 @@ impl Lexer {
             return None;
         }
 
-        self.advance(); // consume closing "
+        self.advance(); // consume closing quote
 
         Some(Token {
             kind: TokenKind::String(value),
@@ -522,6 +524,60 @@ mod tests {
         assert!(errors[0].to_string().contains("Unknown escape"));
     }
 
+    // ----- single-quoted strings -----
+
+    #[test]
+    fn single_quoted_string() {
+        let kinds = tokenize("'hello'");
+        assert_eq!(kinds, vec![TokenKind::String("hello".into())]);
+    }
+
+    #[test]
+    fn single_quoted_empty_string() {
+        let kinds = tokenize("''");
+        assert_eq!(kinds, vec![TokenKind::String("".into())]);
+    }
+
+    #[test]
+    fn single_quoted_with_escape() {
+        let kinds = tokenize("'a\\'b'");
+        assert_eq!(kinds, vec![TokenKind::String("a'b".into())]);
+    }
+
+    #[test]
+    fn single_quoted_with_newline_escape() {
+        let kinds = tokenize("'a\\nb'");
+        assert_eq!(kinds, vec![TokenKind::String("a\nb".into())]);
+    }
+
+    #[test]
+    fn mixed_quote_strings() {
+        let kinds = tokenize("\"double\" 'single'");
+        assert_eq!(kinds, vec![
+            TokenKind::String("double".into()),
+            TokenKind::String("single".into()),
+        ]);
+    }
+
+    #[test]
+    fn single_quote_can_contain_double_quote() {
+        let kinds = tokenize("'he\"llo'");
+        assert_eq!(kinds, vec![TokenKind::String("he\"llo".into())]);
+    }
+
+    #[test]
+    fn double_quote_can_contain_single_quote() {
+        let kinds = tokenize("\"it's\"");
+        assert_eq!(kinds, vec![TokenKind::String("it's".into())]);
+    }
+
+    #[test]
+    fn unterminated_single_quoted_string() {
+        let (_, errors) = tokenize_full("'unterminated");
+        assert_eq!(errors.len(), 1);
+        assert!(errors[0].to_string().contains("Unterminated"));
+    }
+
     // ----- identifiers and keywords -----
 
     #[test]