If either first or last is less than zero, it is considered to refer to before the first element of the list. This allows lreplace to prepend elements to list. If either first or last indicates a position greater than the index of the last element of the list, it is treated as if it is an index one greater than the last element. This allows lreplace to append elements to list.
If last is less than first, then any specified elements will be inserted into the list before the element specified by first with no elements being deleted.
The element arguments specify zero or more new elements to be added to the list in place of those that were deleted. Each element argument will become a separate element of the list. If no element arguments are specified, then the elements between first and last are simply deleted.
% lreplace {a b c d e} 1 1 foo
a foo c d e
Replacing two elements of a list with three:
% lreplace {a b c d e} 1 2 three more elements
a three more elements d e
Deleting the last element from a list in a variable:
% set var {a b c d e}
a b c d e
% set var [lreplace $var end end]
a b c d
A procedure to delete a given element from a list:
proc lremove {listVariable value} {
upvar 1 $listVariable var
set idx [lsearch -exact $var $value]
set var [lreplace $var $idx $idx]
}
Appending elements to the list; note that end+2 will initially be treated as if it is 6 here, but both that and 12345 are greater than the index of the final item so they behave identically:
% set var {a b c d e}
a b c d e
% set var [lreplace $var 12345 end+2 f g h i]
a b c d e f g h i