Changing item in list by index in TCL - arrays

Question

Im trying to work with this awful language and I have to change an item of list by accessing to it with index
set FileRead [open "$flPath" r]
set Data [read $FileRead]
set DataList [split $Data "\n"] #Guess that it creates a list, not an array right?
for {set i 1} { $i < [llength $DataList]} {incr i} {
set line [lindex $DataList $i]
#Some changes on $line
lreplace $DataList $i $line # Thought this should replace the DataList[$i] with my $line
}
I dont understand the awful syntax of TCL! How can I realise it?

Answer 1

You shouldn't just call a language awful because you don't know how to use it, otherwise, just don't use it at all...
In any case, you should read the documentation of lreplace. You supply:
lreplace list first last ?element element ...?
To replace the line in the list of DataList, you thus should change your line to:
lreplace $DataList $i $i $line
This will replace the ith item in DataList with the string in line.
However, this will not change the list DataList at all you need to set the result of the lreplace to a variable (lreplace does not alter the list DataList directly) like...
set DataList [lreplace $DataList $i $i $line]
Though if you are changing only one item in the list at a time, it would be better to use lset:
set FileRead [open "$flPath" r]
set Data [read $FileRead]
set DataList [split $Data "\n"] #Guess that it creates a list, not an array right?
for {set i 1} { $i < [llength $DataList]} {incr i} {
set line [lindex $DataList $i]
# Some changes on $line
lset DataList $i $line
}
lset unlike lreplace does not need to be set since it changes the list in addition to returning the substituted list.

Answer 2

If you are changing every item in a list, and the new value can be produced by a simple script, lmap (list map) is the way to go. The command creates a list with the same number of items as the original list, where each item in the new list has the value of the script with the value of the corresponding item in the original list inserted. Say you want to count characters for each item in a list:
set list [list can be produced]
lmap item $list {
list $item [string length $item]
}
# => {{can 3} {be 2} {produced 8}}
Note that this command does not change the value of list: you need to assign it back to update the value.
The linsert (list insert) adds new items to a list without removing any of the existing elements:
set list [list can be produced]
linsert $list 1 not
# => {can not be produced}
The lreplace (list replace) is mostly useful for insertions that change the number of elements in a list:
set list [list can be produced]
lreplace $list 0 1 can sometimes but not always be
# => {can sometimes but not always be produced}
set list [list the new value can be produced]
lreplace $list 1 1
# => {the value can be produced}
Again, the value of list isn't changed by linsert or lreplace.
If you want to change an item in a list in place, lset (list set) is your friend:
set list [list the new value can be produced]
lset list 1 correct
# => {the correct value can be produced}
This command does change the value of list, because it belongs to the family of setting commands that take a variable name rather than a variable value, and modify the value in some way.
Documentation: linsert, list, lmap, lreplace, lset, set, string