function factory( k, lambda ) {
	if (
		isnan( k ) ||
		isnan( lambda ) ||
		k <= 0.0 ||
		lambda <= 0.0
	) {
		return constantFunction( NaN );
	}
	return logcdf;

	/**
	* Evaluates the natural logarithm of the cumulative distribution function (CDF) for a Weibull distribution.
	*
	* @private
	* @param {number} x - input value
	* @returns {number} evaluated logCDF
	*
	* @example
	* var y = logcdf( 2.0 );
	* // returns <number>
	*/
	function logcdf( x ) {
		var p;
		if ( isnan( x ) ) {
			return NaN;
		}
		if ( x < 0.0 ) {
			return NINF;
		}
		p = -pow( x / lambda, k );
		return ( p < LNHALF ) ? log1p( -exp( p ) ) : ln( -expm1( p ) );
	}
}
Returns a function for evaluating the natural logarithm of the cumulative distribution function (CDF) for a Weibull distribution.

@param {PositiveNumber} k - shape parameter
@param {PositiveNumber} lambda - scale parameter
@returns {Function} logCDF

@example
var logcdf = factory( 2.0, 10.0 );
var y = logcdf( 12.0 );
// returns ~-0.27

y = logcdf( 8.0 );
// returns ~-0.749