wasm2c/examples/fac/fac.wat

(func (export "fac") (param i32) (result i32)
  (if (result i32) (i32.eq (local.get 0) (i32.const 0))
    (then (i32.const 1))
    (else
      (i32.mul (local.get 0) (call 0 (i32.sub (local.get 0) (i32.const 1))))
    )
  )
)