Run Bytecodes with Callback

The standard Vm::eval and Vm::eval_with_scope path is enough for ordinary scripts.

A Rhai Grain bytecodes program becomes a special case when it creates or receives a function pointer that a native Rust function later calls.

Vm::eval_with_callbacks

This is the purpose of Vm::eval_with_callbacks: it registers a native wrapper for each transpiled function for the duration of the run, so a script that creates a closure and then hands it to a host callback can still be resolved by Rhai.

This is necessary when the script does something like:

let values = [1, 2, 3];     // an array

values.map(|x| x * 2);      // native function 'map' taking closure as callback

The Engine must be able to resolve that function pointer within the native Rust call.

Run with Callback Wrappers

use rhai::grain::{Compiler, Vm};

let engine = Engine::new();
let ast = engine.compile(script)?;

// Transpile into shared bytecodes.
let grain = Compiler::new();
let bytecodes = grain.compile(&ast).into_shared();

// Use 'eval_with_callbacks'.
let mut vm = Vm::new(&engine);
let value = vm.eval_with_callbacks(&mut scope, &bytecodes)?;