[Unicon-group] Object to manage a list, with capability to reorder a member?

[Art Eschenlauer]

Dear Uniconers:

For a particular program that I am writing, I created a class (OList, 
see code at end of message) to manage a list. If anyone knows of a 
better or more general implementation, I'd like to hear about it.

Anyway, I am looking at the l_reorder() method, which moves the list 
item at position specified by the first argument to the position 
specified by the second argument. To clarify what I mean,
  object := OList( [1,2,3,4,5] )
  # object.data is now [1,2,3,4,5]
  # next, move data[-2:+1] to the position data[2]
  object.l_reorder( -2, 2 )
  # object.data is now [1,4,2,3,5]

My question is, "Is there a way to do this that is more straightforward 
than using delete and insert?" For instance, exchanging items could 
straightforwardly be coded in a method body as
  return (data[imove] :=: data[ib4]) & 1
but I cannot think of an equally terse way of moving a data item.

Thanks for your insight.

-Art

class OList ( # class to handle both categories and subcategories
  data # holds the list itself
 )
  method l_delete( # remove an object from the list
     ib4 # index of object to delete
    )
     local length
     length := *data
     (0 > ib4) & ib4 +:= length + 1     # make sure ib4 >0
     0 <= ib4 <= length | fail          # reject ib4 out of range
     return delete( data, ib4 ) & 1
  end
  method l_get_copy( # get a copy of the data member
    )
     return copy(data)
  end
  method l_insert( # insert an object into the list
     ib4, # the position in the list before which the object should be 
inserted
     o    # an object to append to the list
    )
     local length
     length := *data
     (0 > ib4) & ib4 +:= length + 1     # make sure ib4 > 0
     0 <= ib4 <= length | fail          # reject ib4 out of range
     return insert( data, ib4, o ) & 1
  end
  method l_reorder( # change the order of items in the list
     imove, # index of the item to move
     ib4    # index before which item should be moved
    )
     local item, length
     length := *data
     (0 > ib4) & ib4 +:= length + 1     # make sure ib4 > 0
     0 <= ib4 <= length | fail          # reject ib4 out of range
     (0 > imove) & imove +:= length + 1 # make sure imove > 0
     0 < imove <= length | fail         # reject imove out of range
     item := data[imove]
     delete( data, imove )
     insert( data, imove >= ib4 | (0 < ib4) - 1 , item) | put( data, item )
     return
  end
  method l_set( # set the data member to the list supplied
     d_list # data to store in data member
    )
     return ( type(d_list)=="list", data := d_list )
     stop( "OList.lset() failed - was argument a list?" )
  end
 initially( l )
     l_set( l )
end





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