Parens free `switch` expression

switch.macro.sjs

/*

Multiple expressions per case are allowed

The result of the matching case, or the optional default, is automatically returned

```
var x = switch os {
  case 'osx', 'ios': 'apple'
  default: os
};
```

*/

let switch = macro {
  rule { $value:expr { $body ... } } => {
    (function () {
      switch ($value) {
        $body ...
      }
    })()
  }
}

let case = macro {
  rule { $($pattern:expr (,) ...): $return:expr } => {
    $(case $pattern:) ...
      return $return
  }
}

let default = macro {
  rule { : $return:expr } => {
    default:
      return $return
  }
}

export switch;
export case;
export default;