function go(code) {
    assert(consumed === true, 'expected character to be consumed')
    consumed = undefined
    debug('main: passing `%s` to %s', code, state && state.name)
    expectedCode = code
    assert(typeof state === 'function', 'expected state')
    state = state(code)
  }
Deal with one code.

@param {Code} code
  Code.
@returns {undefined}
  Nothing.