collect(a) := block(
   [n: length(a), b: [ ], x: a[1], m: 1],
   for i from 2 thru n do
      (if a[i] = x then m: m + 1 else (b: endcons([x, m], b), x: a[i], m: 1)),
   b: endcons([x, m], b)
)$

look_and_say(s) := apply(sconcat, map(lambda([p], sconcat(string(p[2]), p[1])), collect(charlist(s))))$

block([s: "1"], for i from 1 thru 10 do (disp(s), s: look_and_say(s)));
/* "1"
   "11"
   "21"
   "1211"
   "111221"
   "312211"
   "13112221"
   "1113213211"
   "31131211131221"
   "13211311123113112211" */