Module CheckIt {
      Null=(,)
      Tree=((((Null,7,Null),4,Null),2,(Null,5,Null)),1,(((Null,8,Null),6,(Null,9,Null)),3,Null))

      Module preorder (T) {
            Print "preorder:    ";
            printtree(T)
            Print
            sub printtree(T)
                  Print T#val(1);" ";
                  If len(T#val(0))>0 then printtree(T#val(0))
                  If len(T#val(2))>0 then printtree(T#val(2))
            end sub
      }
      preorder Tree

      Module inorder (T) {
            Print "inorder:     ";
            printtree(T)
            Print
            sub printtree(T)
                  If len(T#val(0))>0 then printtree(T#val(0))
                  Print T#val(1);" ";
                  If len(T#val(2))>0 then printtree(T#val(2))
            end sub
      }
      inorder Tree

      Module postorder (T) {
            Print "postorder:   ";
            printtree(T)
            Print
            sub printtree(T)
                  If len(T#val(0))>0 then printtree(T#val(0))
                  If len(T#val(2))>0 then printtree(T#val(2))
                  Print T#val(1);" ";
            end sub
      }
      postorder Tree

      Module level_order (T) {
            Print "level-order: ";
            Stack New {
                  printtree(T)
                  if empty then exit
                  Read T
                  Loop
            }
            Print
            sub printtree(T)
                  If Len(T)>0 then
                        Print T#val(1);" ";
                        Data T#val(0), T#val(2)
                  end if
            end sub
      }
      level_order Tree
}
CheckIt