/*REXX program to show anonymous recursion of a function or subroutine with memoization.*/
numeric digits 1e6                               /*in case the user goes ka-razy with X.*/
parse arg x .                                    /*obtain the optional argument from CL.*/
if x=='' | x==","  then x= 12                    /*Not specified?  Then use the default.*/
@.= .;     @.0= 0;      @.1= 1                   /*used to implement memoization for FIB*/
w= length(x)                                     /*W:  used for formatting the output.  */
                   do j=0  for x+1               /*use the  argument  as an upper limit.*/
                   say 'fibonacci('right(j, w)") ="   fib(j)
                   end  /*j*/                    /* [↑] show Fibonacci sequence: 0 ──► X*/
exit 0                                           /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
fib: procedure expose @.; arg z;  if z>=0  then return .(z)
                          say "***error***  argument can't be negative.";   exit
.: procedure expose @.; arg #; if @.#\==.  then return @.#;  @.#=.(#-1)+.(#-2); return @.#