Passing a list to a proc tcl

Question

I already looked at Passing list to Tcl procedure, and I couldn't quite understand how to do it properly. To put it in context, this is how I'm passing the list:

switch $choice {
    n {
        set ptable [new_partition {$ptable}]
    }
    d {
        set ptable [delete_partition {$ptable}]
    }
    p {
        set ptable [print_table {$ptable}]
    }
    w {
        set ptable [write_table {$ptable $fn}]
        puts "Saving file...\nExiting..."
        break
    }
    q {
        puts "Exiting..."
        break
    }
    default {
        puts "Illegal option"
    }
}

This is an example of one of the procedures

proc print_table {ptable} {
    # Set format string
    set formatStr {%-16s%-8s%-8s%-8s%-8s%-8s}
    # Print the contents of ptable to stdout
    puts [format $formatStr "\nPartition" "Start" "End" "Blocks" "ID" "System"]
    puts "--------------------------------------------------------"
    foreach item $ptable {
        set parts [lindex $item 0]
        set sCyl [lindex $item 1]
        set eCyl [lindex $item 2]
        set blok [lindex $item 3]
        set id [lindex $item 4]
        set sys [lindex $item 5]
        puts [format $formatStr $parts $sCyl $eCyl $blok $id $sys]
    }
    return $ptable
}

Ptable is being created correctly, but it loses all its information as soon as I pass it to one of the procedures. I've tried passing it with "{*}$ptable" but it returns an error. Everything else in my program is working perfectly (if I take the code from any single procedure and put it by itself, it all works), I just can't seem to get it to pass the list properly.

Answer 1

Don't use braces here: new_partition {$ptable} -- braces inhibit variable expansion, and you are passing the 7-character string $ptable

See rule #6 in http://tcl.tk/man/tcl8.6/TclCmd/Tcl.htm

Just pass the variable: new_partition $ptable

Similarly:

delete_partition $ptable
print_partition $ptable
write_partition $ptable $fn

---

The print_table procedure you've shown does not actually modify the argument you pass to it, so you don't really need to return a value. Also, you don't really need to decompose the rows of ptable into individual variables if you're just passing them to format. You can turn that proc into

# Print the contents of ptable to stdout
proc print_table {ptable} {
    set formatStr {%-16s%-8s%-8s%-8s%-8s%-8s}
    puts [format $formatStr "\nPartition" Start End Blocks ID System]
    puts "--------------------------------------------------------"
    foreach item $ptable {
        puts [format $formatStr {*}$item]
    }
}

And don't do this

set ptable [print_table $ptable]

but do this

print_table $ptable