Is there any existing solution to move list number backwards, forwards in a list?

[Jean Louis]

For purposes of changing priorities of objects in a set, I need to
move single item in a list backwards and forwards.

Let us say item is number 7 in following list:

'(1 2 3 4 5 6 7 8 9)

Then I wish to move item number 7 to different number and renumber all
items so that number 7 becomes number 6 and number 6 comes in the
place of number 7.

Situation is more complex, each object ID has its priority like one of
those in the list. So each object ID has to be updated with its
priority when I press single click.

As it looks somehow common to me, maybe somebody knows if something
like that exists as a package.


Jean

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