harmonic-progression with automatic :size

Perhaps it would be possible to make the harmonic progression function have the option of counting the size based on the interval inputted by the user?

Under certain circumstances, it's useful to specify the size, but under other circumstances, it's a bit cumbersome.

I've made my own simple version that does this (but doesn't include all the options of the original function). I called bass-progression. 

(defun bass-progression (progression steps scale)
  (harmonic-progression progression scale
   :size (loop for i in steps collect (+ (length i) 1))
   :step steps))

Example: 

(bass-progression '(0 1 2 3 4) '((2) (2 3) (2 3 4) (2 3 4 5)) '(c major))
=> (c4e4 d4f4b4 e4g4d5g5 f4a4f5c6f6 g4b4)