Parens free `unless` statement, the opposite of `if`

unless.macro.sjs

/*

`unless cond {}` is equivalent to `if !(cond) {}`

Brackets are mandatory, except when `unless` is followed by specials keywords (return, break and continue)

```
unless cond return
unless cond break [label]
unless cond continue [label]
```

*/

macro unless {
  rule { $cond:expr { $body ... } } => {
    if (!$cond) { $body ... }
  }
  rule { $cond ; } => {
  	if (!$cond);
  }
  rule { $cond:expr return $return:expr } => {
  	if (!$cond) return $return
  }
  rule { $cond:expr return } => {
  	if (!$cond) return
  }
  rule { $cond:expr continue $label:ident } => {
  	if (!$cond) continue $label
  }
  rule { $cond:expr continue } => {
  	if (!$cond) continue
  }
  rule { $cond:expr break $label:ident } => {
  	if (!$cond) break $label
  }
  rule { $cond:expr break } => {
  	if (!$cond) break
  }
  rule { $cond:expr do $body } => {
  	if (!$cond) do $body
  }
}

export unless;