Source code in the icon programming language

procedure main()                     #: demonstrate various ways to sort a list and string 
   demosort(heapsort,[3, 14, 1, 5, 9, 2, 6, 3],"qwerty")
end

procedure heapsort(X,op)                            #: return sorted list ascending(or descending)
local head,tail

   op := sortop(op,X)                               # select how and what we sort

   every head := (tail := *X) / 2  to 1 by -1 do    # work back from from last parent node
      X := siftdown(X,op,head,tail)                 # sift down from head to make the heap 

   every tail := *X to 2 by -1 do {                 # work between the beginning and the tail to final positions
      X[1] :=: X[tail]
      X := siftdown(X,op,1,tail-1)                  # re-sift next (previous) branch after shortening the heap
      }

   return X
end

procedure siftdown(X,op,root,tail)                  #: the value @root is moved "down" the path of max(min) value to its level
local child

   while (child :=  root * 2) <= tail do {          # move down the branch from root to tail

      if op(X[child],X[tail >= child + 1]) then     # choose the larger(smaller) 
         child +:= 1                                # ... child 

      if op(X[root],X[child]) then  {               # root out of order? 
         X[child] :=: X[root]                       
         root := child                              # follow max(min) branch
         }
      else 
         return X
      }
   return X
end