Passing list to Tcl procedure

Question

What is the canonical way to pass a list to a Tcl procedure?

I\'d really like it if I could get it so that a list is automatically expanded into a variable number of arg

Answer 1

It depends on the version of Tcl you're using, but: For 8.5:

set mylist {a b c}
myprocedure option1 option2 {*}$mylist

For 8.4 and below:

set mylist {a b c}
eval myprocedure option1 option2 $mylist
# or, if option1 and 2 are variables
eval myprocedure [list $option1] [list $option2] $mylist
# or, as Bryan prefers
eval myprocedure \$option1 \$option2 $mylist

Answer 2

It might be useful to note that passing your command to catch will also solve this problem:

set a {b c}
if [catch "myprocedure option1 option2 $a"] {
    # handle errors
}

This should probably only be used if you want to handle errors in myprocedure at this point in your code so that you don't have to worry about rethrowing any errors that get caught.

Answer 3

To expand on RHSeeger's answer, you would code myprocedure with the special args argument like this:

proc myprocedure {opt1 opt2 args} {
    puts "opt1=$opt1"
    puts "opt2=$opt2"
    puts "args=[list $args]" ;# just use [list] for output formatting
    puts "args has [llength $args] elements"
}