Question

Say I have a TCL list:

set myList {}
lappend myList [list a b 1]
lappend myList [list c d 2]
.....

Now I want to modify the list like this:

foreach item $myList {
lappend item "new"
}

But at the end I have not modified list. Why? item is a reference on the list item no?

Answer 1

item is not a reference to the list item. It is a copy. To do what you want, you could do this:

set newlist {}
foreach item $myList {
  lappend item "new"
  lappend newlist $item
}
set mylist $newlist