cfeval(x) := block([a, b, n, z], a: x[1], b: x[2], n: length(a), z: 0,
   for i from n step -1 thru 2 do z: b[i]/(a[i] + z), a[1] + z)$

cf_sqrt2(n) := [cons(1, makelist(2, i, 2, n)), cons(0, makelist(1, i, 2, n))]$

cf_e(n) := [cons(2, makelist(i, i, 1, n - 1)), append([0, 1], makelist(i, i, 1, n - 2))]$

cf_pi(n) := [cons(3, makelist(6, i, 2, n)), cons(0, makelist((2*i - 1)^2, i, 1, n - 1))]$

cfeval(cf_sqrt2(20)), numer;   /* 1.414213562373097 */
% - sqrt(2), numer;            /* 1.3322676295501878*10^-15 */

cfeval(cf_e(20)), numer;       /* 2.718281828459046 */
% - %e, numer;                 /* 4.4408920985006262*10^-16 */

cfeval(cf_pi(20)), numer;      /* 3.141623806667839 */
% - %pi, numer;                /* 3.115307804568701*10^-5 */


/* convergence is much slower for pi */
fpprec: 20$
x: cfeval(cf_pi(10000))$
bfloat(x - %pi);               /* 2.4999999900104930006b-13 */