Re: Sort a list of dotted pairs

Scheme's list-sort (R6RS) takes a comparison function that's used to
compare elements of the list.  So,
(list-sort < '(5 4 3 1 2))
=>
(1 2 3 4 5).

Now expand this a bit by making < an explicit lambda:
(list-sort (lambda (x y) (< x y)) '(5 4 3 1 2))
=>
(1 2 3 4 5)

So, how do we sort a list of strings by their lengths?
(list-sort
  (lambda (x y) (< (string-length x) (string-length y)))
  '("bbb" "ddddd" "ccc" "a"))
=>
("a" "bbb" "ccc" "ddddd")

So, how do we sort a list of pairs by the numeric values of their
cars?