add: more samples and make them work

rpgrt/src/lib.rs

@@ -156,6 +156,59 @@ pub extern "C" fn rpg_dsply_f64(f: f64) {
     let _ = out.flush();
 }
 
+// ─────────────────────────────────────────────────────────────────────────────
+// rpg_dsply_read — display a prompt and read an integer response from stdin
+// ─────────────────────────────────────────────────────────────────────────────
+
+/// Display `prompt` (a null-terminated C string) with a `DSPLY` prefix, then
+/// read one line from stdin and parse it as a signed 64-bit integer.  The
+/// parsed value is written through `response`.
+///
+/// This implements the three-operand form of the `DSPLY` opcode:
+/// ```rpg
+/// Dsply prompt ' ' response_var;
+/// ```
+/// where the third operand is the variable that receives the operator's reply.
+///
+/// If stdin is exhausted (EOF) or the line cannot be parsed as an integer the
+/// response is left unchanged.
+///
+/// # Safety
+///
+/// * `prompt` must be a valid null-terminated C string (or null, treated as
+///   an empty string).
+/// * `response` must be a valid, aligned, writable pointer to an `i64`.
+#[no_mangle]
+pub unsafe extern "C" fn rpg_dsply_read(
+    prompt: *const std::os::raw::c_char,
+    response: *mut i64,
+) {
+    use std::io::BufRead;
+
+    // Display the prompt.
+    let text = if prompt.is_null() {
+        std::borrow::Cow::Borrowed("")
+    } else {
+        unsafe { CStr::from_ptr(prompt).to_string_lossy() }
+    };
+    {
+        let stdout = io::stdout();
+        let mut out = stdout.lock();
+        let _ = writeln!(out, "DSPLY  {}", text);
+        let _ = out.flush();
+    }
+
+    // Read one line from stdin and parse it as i64.
+    let stdin = io::stdin();
+    let mut line = String::new();
+    if stdin.lock().read_line(&mut line).is_ok() {
+        let trimmed = line.trim();
+        if let Ok(n) = trimmed.parse::<i64>() {
+            unsafe { *response = n; }
+        }
+    }
+}
+
 // ─────────────────────────────────────────────────────────────────────────────
 // rpg_halt — abnormal termination
 // ─────────────────────────────────────────────────────────────────────────────