Add all the A tasks

Task/Apply-a-callback-to-an-array/REXX/apply-a-callback-to-an-array.rexx

@@ -0,0 +1,29 @@
+/*REXX program to apply a  callback  to a  stemmed  (REXX)  array.      */
+        a.=;   b.=
+ a.0= 0
+ a.1= 1
+ a.2= 2
+ a.3= 3
+ a.4= 4
+ a.5= 5
+ a.6= 6
+ a.7= 7
+ a.8= 8
+ a.9= 9
+a.10=10
+
+call listab 'before'
+call bangit 'a','b'      /*factorialize the A array, store results in B */
+call listab ' after'
+exit                                   /*stick a fork in it, we're done.*/
+/*──────────────────────────────────BANGIT subroutine───────────────────*/
+bangit:   do i=0
+          _=value(arg(1)'.'i);    if _=='' then return
+          call value arg(2)'.'i,fact(_)
+          end    /*i*/
+/*──────────────────────────────────FACT subroutine─────────────────────*/
+fact: procedure; !=1; do j=2 to arg(1); !=!*j; end; return !
+/*──────────────────────────────────LISTAB subroutine───────────────────*/
+listab: do j=0  while a.j\=='';     say arg(1) 'a.'j"="a.j;     end  /*j*/
+say;    do k=0  while b.k\=='';     say arg(1) 'b.'k"="b.k;     end  /*k*/
+return