cond, almost like in lisp

cond.js

/**
   @example:
   ```javascript
   const result = cond(
     [false,     () => 'this should not be'],
     [Boolean(), () => 'Boolean defaults to false'],
     [true,      () => '`true` can be considered the "catch all" symbol in a cond expr.']
   );
   ```
   
   ```javascript
   const fibonacci = function fib(n) {
     return cond(
       [n === 0, () => 0],
       [n === 1, () => 1],
       [true,    () => fib(n - 1) + fib(n - 2)]
     );
   };

   const result = fibonacci(7); // -> 13
   ```
 */
export default function cond(...conditions) {
  // loop over each of the conditions.
  for (let [test, fn] of conditions) {
    if (test) {
      return fn();
    }
  }

  // let off a warning, because falling through
  // in a cond should be considered undefined behaviour.
  console.warn(new Error('no conds matched'));
  return void 0;
};