Fix README example for on_print and on_debug.

README.md

@@ -1979,17 +1979,20 @@ engine.on_print(|x| println!("hello: {}", x));
 engine.on_debug(|x| println!("DEBUG: {}", x));
 
 // Example: quick-'n-dirty logging
-let mut log: Vec<String> = Vec::new();
+let logbook = Arc::new(RwLock::new(Vec::<String>::new()));
 
 // Redirect print/debug output to 'log'
-engine.on_print(|s| log.push(format!("entry: {}", s)));
-engine.on_debug(|s| log.push(format!("DEBUG: {}", s)));
+let log = logbook.clone();
+engine.on_print(move |s| log.write().unwrap().push(format!("entry: {}", s)));
+
+let log = logbook.clone();
+engine.on_debug(move |s| log.write().unwrap().push(format!("DEBUG: {}", s)));
 
 // Evaluate script
 engine.eval::<()>(script)?;
 
-// 'log' captures all the 'print' and 'debug' output
-for entry in log {
+// 'logbook' captures all the 'print' and 'debug' output
+for entry in logbook.read().unwrap().iter() {
     println!("{}", entry);
 }
 ```

tests/print.rs

@@ -0,0 +1,31 @@
+use rhai::{Engine, EvalAltResult};
+use std::sync::{Arc, RwLock};
+
+#[test]
+fn test_print() -> Result<(), Box<EvalAltResult>> {
+    let mut engine = Engine::new();
+
+    let logbook = Arc::new(RwLock::new(Vec::<String>::new()));
+
+    // Redirect print/debug output to 'log'
+    let log = logbook.clone();
+    engine.on_print(move |s| log.write().unwrap().push(format!("entry: {}", s)));
+
+    let log = logbook.clone();
+    engine.on_debug(move |s| log.write().unwrap().push(format!("DEBUG: {}", s)));
+
+    // Evaluate script
+    engine.eval::<()>("print(40 + 2)")?;
+    engine.eval::<()>(r#"debug("hello!")"#)?;
+
+    // 'logbook' captures all the 'print' and 'debug' output
+    assert_eq!(logbook.read().unwrap().len(), 2);
+    assert_eq!(logbook.read().unwrap()[0], "entry: 42");
+    assert_eq!(logbook.read().unwrap()[1], r#"DEBUG: "hello!""#);
+
+    for entry in logbook.read().unwrap().iter() {
+        println!("{}", entry);
+    }
+
+    Ok(())
+}