Add an example of namespaced APIs

By creating wasm modules from Rust!

examples/wasm-in-wasm/src/lib.rs

@@ -0,0 +1,54 @@
+#![feature(proc_macro)]
+
+extern crate wasm_bindgen;
+
+use wasm_bindgen::prelude::*;
+
+// Like with the `dom` example this block will eventually be auto-generated, but
+// for now we can write it by hand to get by!
+#[wasm_bindgen]
+extern {
+    type Module;
+    #[wasm_bindgen(constructor, js_namespace = WebAssembly)]
+    fn new(data: &[u8]) -> Module;
+
+    type Instance;
+    #[wasm_bindgen(constructor, js_namespace = WebAssembly)]
+    fn new(module: Module) -> Instance;
+    #[wasm_bindgen(method, getter, js_namespace = WebAssembly)]
+    fn exports(this: &Instance) -> Exports;
+
+    type Exports;
+    #[wasm_bindgen(method, structural)]
+    fn add(this: &Exports, a: u32, b: u32) -> u32;
+    #[wasm_bindgen(method, getter, structural)]
+    fn memory(this: &Exports) -> Memory;
+
+    type Memory;
+    #[wasm_bindgen(method, js_namespace = WebAssembly)]
+    fn grow(this: &Memory, amt: u32) -> u32;
+
+    #[wasm_bindgen(js_namespace = console)]
+    fn log(a: &str);
+}
+
+macro_rules! println {
+    ($($t:tt)*) => (log(&format_args!($($t)*).to_string()))
+}
+
+const WASM: &[u8] = include_bytes!("add.wasm");
+
+#[wasm_bindgen]
+pub fn run() {
+    println!("instantiating a new wasm module directly");
+    let a = Module::new(WASM);
+    let b = Instance::new(a);
+    let c = b.exports();
+
+    println!("1 + 2 = {}", c.add(1, 2));
+    let mem = c.memory();
+    println!("created module has {} pages of memory", mem.grow(0));
+    println!("giving the module 4 more pages of memory");
+    mem.grow(4);
+    println!("now the module has {} pages of memory", mem.grow(0));
+}