applied cargo fmt, cleaned project root.

Author: RafaelLopes23

README.md

@@ -206,7 +206,7 @@ Metabuiltins are functions implemented in Rust and exposed to user code. They ha
 
 | Function                      | Description                                                       |
 |-------------------------------|-------------------------------------------------------------------|
-| `open(path, mode?, content?)` | Open a file. Modes: `r` (read), `w` (write), `a` (append).        |
+| `open(path, mode, content)` | Open a file. Modes: `r` (read), `w` (write), `a` (append).        |
 
 ---
 

examples/hello_io.rpy

@@ -152,4 +152,15 @@ asserteq(5 * 5, 25, "5 * 5 should equal 25");
 assertneq(10, 20, "10 should not equal 20");
 var _ = print_line("All assertions passed!");
 
+var _ = print_line("=== 15. File I/O ===");
+val test_file = "examples/rpython_test.txt";
+var _ = open(test_file, "w", "Hello from RPython!");
+var _ = print("Wrote to file. Reading back: ");
+val contents = open(test_file, "r");
+var _ = print_line(contents);
+var _ = open(test_file, "a", "Appended line.");
+val contents2 = open(test_file, "r");
+var _ = print("After append: ");
+var _ = print_line(contents2);
+
 var _ = print_line("=== Demo Complete ===");

examples/rpython_test.txt

@@ -0,0 +1 @@
+Hello from RPython!Appended line.

src/main.rs

@@ -57,4 +57,4 @@ fn main() {
             std::process::exit(1);
         }
     }
-}
+}