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Task/Ackermann-function/REXX/ackermann-function-1.rexx

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+/*REXX program calculates/shows some values for the Ackermann function. */
+
+                     /*Note: the Ackermann function (as implemented) is */
+                     /*      higly recursive and is limited by the      */
+                     /*      biggest number that can have "1" added to  */
+                     /*      a number (successfully, accurately).       */
+high=24
+         do j=0 to 3;   say
+              do k=0 to high%(max(1,j))
+              call Ackermann_tell j,k
+              end   /*k*/
+         end        /*j*/
+exit                                   /*stick a fork in it, we're done.*/
+/*──────────────────────────────────ACKERMANN_TELL subroutine───────────*/
+ackermann_tell: parse arg mm,nn;   calls=0    /*display an echo message.*/
+nnn=right(nn,length(high))
+say 'Ackermann('mm","nnn')='right(ackermann(mm,nn),high),
+                             left('',12) 'calls='right(calls,high)
+return
+/*──────────────────────────────────ACKERMANN subroutine────────────────*/
+ackermann: procedure expose calls      /*compute the Ackerman function. */
+parse arg m,n;      calls=calls+1
+if m==0 then return n+1
+if n==0 then return ackermann(m-1,1)
+             return ackermann(m-1,ackermann(m,n-1))