function next( error ) {
		var i;
		if ( error ) {
			return done( error );
		}
		idx += 1;

		// Cache the most recent results...
		if ( arguments.length > 1 ) {
			args = new Array( arguments.length-1 );
			for ( i = 1; i < arguments.length; i++ ) {
				args[ i-1 ] = arguments[ i ];
			}
		}
		// Run the test condition:
		predicate( idx, onPredicate );
	}
Callback invoked upon completion of a provided function.

@private
@param {(Error|null)} error - error object
@param {...*} results - function results
@returns {void}