chickadee » ck-macros » c-u-

Unary subtraction. Drops an element from the front of the first list for each element in second list, then yields the remaining list. Negative numbers cannot be represented in unary, so this yields '() if the second list is equal or longer than the first.

(ck () (c-quote (c-u- (c-list 'a 'b 'c 'd) '(x y))))
;; ==> '(c d)

(ck () (c-quote (c-u- (c-list 'a 'b) (c-list 'x 'y 'z))))
;; ==> '()
;; Because negative numbers cannot be represented in unary.