Creates a new sampled PDF object with the specified dimension, samples environment creation procedure that follows the API of rb-tree, and weighted samples. The samples can be specified in one of two ways. If both XS and WS are provided, then XS is a sequence that contains the samples, and WS is a sequence that contains the corresponding weights. If only XS is provided, or WS is false, then XS must consist of cons cells, where the car is the weight, and the cdr is the sample. Optional arguments XCAR XCDR XNULL? could be used for sequences other than lists (e.g. streams).