function factory( lambda ) {
	if ( lambda < 0.0 || lambda === PINF || isnan( lambda ) ) {
		return constantFunction( NaN );
	}
	return quantile;

	/**
	* Evaluates the quantile function for an exponential distribution.
	*
	* @private
	* @param {Probability} p - input value
	* @returns {number} evaluated quantile function
	*
	* @example
	* var y = quantile( 0.3 );
	* // returns <number>
	*/
	function quantile( p ) {
		if ( isnan( p ) || p < 0.0 || p > 1.0 ) {
			return NaN;
		}
		return -ln( 1.0 - p ) / lambda;
	}
}
Returns a function for evaluating the quantile function of an exponential distribution with rate parameter `lambda`.

@param {PositiveNumber} lambda - rate parameter
@returns {Function} quantile function

@example
var quantile = factory( 0.4 );
var y = quantile( 0.4 );
// returns ~1.277

y = quantile( 1.0 );
// returns Infinity