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 arguments.

So that something like:

set a {b c}
myprocedure option1 option2 $a

and

myprocedure option1 option2 b c

are equivalent.

I am sure I saw this before, but I can't find it anywhere online. Any help (and code) to make both cases equivalent would be appreciated.

Is this considered a standard Tcl convention. Or am I even barking up the wrong tree?

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

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"
}