suite.js: `nin` operator macro

nin-macro.js

// Use suite.js to define a JavaScript macro for a "not in" operator
// http://sweetjs.org/

macro nin {
  rule infix {
    $key:expr | $obj:expr
  } => {
    !($key in $obj)
  }
}

// Now,

if (key nin obj) {
  return null;
}

// ...compiles to:

if (!(key in obj)) {
  return null;
}