/* ?? REXX Heap sort ?qx?
 Note that numeric values are sorted numerically, i.e. 0009 > 5
 */

 Call HeapSort 'text.'     /* sort stem TEXT. */
  . . .
Heapsort: arg _heapn .;Return HeapSortX(_heapn)
HeapsortX: Procedure expose (_heapn)     /* Heapsort main */
 arg _heapn .
 m = Value(_heapn'0')
 n = m
 do k=m % 2 to 1 by -1
   call HeapSortD _heapn k n
 end
 do while n>1
   t = Value(_heapn'1')
   zz=Value(_heapn'1',Value(_heapn||n))
   zz=Value(_heapn||n,t)
   n = n-1
   call HeapSortD _heapn 1 n
 end
 return 0
HeapSortD: Procedure expose (_heapn) /* downheap sub of HeapSort */  */
 parse Arg _heapn k n
 v = Value(_heapn||k)
 do while k <= n%2
   j = k+k
   if j < n then do
     i = j+1
     if Value(_heapn||j) < Value(_heapn||i) then j=j+1
   end
   if v >= Value(_heapn||j) then return Value(_heapn||k,v)
   zz=Value(_heapn||k,Value(_heapn||j))
   k = j
 end
 return Value(_heapn||k,v)