wasmtime/docs/wasm-wat.md

WebAssembly Text Format (*.wat)

While not necessarily a full-blown language you might be curious how Wasmtime interacts with the *.wat text format! The wasmtime CLI and Rust embedding API both support the *.wat text format by default.

"Hello, World!" is pretty nontrivial in the *.wat format since it's assembly-like and not really intended to be a primary programming language. That being said we can create a simple add function to call it!

For example if you have a file add.wat like so:

(module
  (func (export "add") (param i32 i32) (result i32)
    local.get 0
    local.get 1
    i32.add))

Then you can execute this on the CLI with:

$ wasmtime add.wat --invoke add 1 2
warning: ...
warning: ...
3

And we can see that we're already adding numbers!

You can also see how this works in the Rust API like so:

# extern crate wasmtime;
# extern crate anyhow;
use wasmtime::*;

# fn main() -> anyhow::Result<()> {
let mut store = Store::<()>::default();
let wat = r#"
  (module
    (func (export "add") (param i32 i32) (result i32)
      local.get 0
      local.get 1
      i32.add))
"#;
let module = Module::new(store.engine(), wat)?;
let instance = Instance::new(&mut store, &module, &[])?;
let add = instance.get_typed_func::<(i32, i32), i32, _>(&mut store, "add")?;
println!("1 + 2 = {}", add.call(&mut store, (1, 2))?);
# Ok(())
# }