function _isRegExp(x) {
    return Object.prototype.toString.call(x) === '[object RegExp]';
  }
Runs the given function with the supplied object, then returns the object.

Acts as a transducer if a transformer is given as second parameter.

@func
@memberOf R
@since v0.1.0
@category Function
@sig (a -> *) -> a -> a
@param {Function} fn The function to call with `x`. The return value of `fn` will be thrown away.
@param {*} x
@return {*} `x`.
@example

     const sayX = x => console.log('x is ' + x);
     R.tap(sayX, 100); //=> 100
     // logs 'x is 100'
@symb R.tap(f, a) = (f(a), a)