use rhai::Engine;

let mut engine = Engine::new();

let ast1 = engine.compile(r#"fn foo(x) { 42 + x } foo(1)"#)?;
let ast2 = engine.compile(r#"fn foo(n) { "hello" + n } foo("!")"#)?;

let ast = ast1.merge(&ast2);    // Merge 'ast2' into 'ast1'

// Notice that using the '+' operator also works:
// let ast = &ast1 + &ast2;

// 'ast' is essentially:
//
//    fn foo(n) { "hello" + n } // <- definition of first 'foo' is overwritten
//    foo(1)                    // <- notice this will be "hello1" instead of 43,
//                              //    but it is no longer the return value
//    foo("!")                  // returns "hello!"

// Evaluate it
assert_eq!(engine.eval_ast::<String>(&ast)?, "hello!");