Source code in the rexx programming language

/*REXX program  converts  Reverse Polish Notation  (RPN)    ───►    an infix notation.  */
showAction = 1                                   /*  0  if no   showActions   wanted.   */
         # = 0                                   /*initialize stack pointer to 0 (zero).*/
        oS = '+ - / * ^'                         /*the operator symbols.                */
        oP = '2 2 3 3 4'                         /*the operator priorities.             */
        oA = '◄ ◄ ◄ ◄ ►'                         /*the operator associations.           */
say  "infix: "   toInfix( "3 4 2 * 1 5 - 2 3 ^ ^ / +" )
say  "infix: "   toInfix( "1 2 + 3 4 + ^ 5 6 + ^" )     /* [↓]  Sprechen Sie Deutsch?   */
say  "infix: "   toInfix( "Mond Sterne Schlamm + * Feur Suppe * ^" )
exit 0                                           /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
pop:       pop= #;                 #= # - 1;                     return @.pop
push:      #= # + 1;               @.#= arg(1);                  return
/*──────────────────────────────────────────────────────────────────────────────────────*/
stack2str: $=;             do j=1  for #;          _ = @.j;      y= left(_, 1)
                           if pos(' ', _)==0  then _ = '{'strip( substr(_, 2) )"}"
                                              else _ =           substr(_, 2)
                           $=$  '{'strip(y _)"}"
                           end   /*j*/
           return space($)
/*──────────────────────────────────────────────────────────────────────────────────────*/
toInfix:   parse arg rpn;   say copies('─', 80 - 1);             say 'RPN: '  space(rpn)

               do N=1  for words(RPN)                  /*process each of the RPN tokens.*/
               ?= word(RPN, N)                         /*obtain next item in the list.  */
               if pos(?,oS)==0  then call push '¥' ?   /*when in doubt, add a Yen to it.*/
                                else do;   g= pop();    gp= left(g, 1);    g= substr(g, 2)
                                           h= pop();    hp= left(h, 1);    h= substr(h, 2)
                                     tp= substr(oP, pos(?, oS),  1)
                                     ta= substr(oA, pos(?, oS),  1)
                                     if hp
                                     if gp
                                     call  push   tp  ||  h  ?  g
                                     end
                if showAction  then say   right(?, 25)    "──►"    stack2str()
                end   /*N*/

           return space( substr( pop(), 2) )