(define make-range
  Start Start -> ["," Start]
  Start End   -> ["," Start "," End] where (= End (+ Start 1))
  Start End   -> ["," Start "-" End])

(define range-extract-0
  Start End []     -> (make-range Start End)
  Start End [A|As] -> (range-extract-0 Start A As) where (= (+ 1 End) A)
  Start End [A|As] -> (append (make-range Start End) (range-extract-0 A A As)))

(define range-extract
  [A |As] -> (FORMAT NIL "~{~a~}" (tail (range-extract-0 A A As))))

(range-extract [ 0  1  2  4  6  7  8 11 12 14
                15 16 17 18 19 20 21 22 23 24
                25 27 28 29 30 31 32 33 35 36
                37 38 39])